Each square represents \(\displaystyle 3\) students. Mr. Ray's bar has \(\displaystyle 4\) squares in it, which means he has \(\displaystyle 12\) students with pets (\(\displaystyle 3\times4=12\)). Ms. Hen's bar has \(\displaystyle 2\) squares in it, which means she has \(\displaystyle 6\) students with pets (\(\displaystyle 3\times2=6\)). 

To find the total in both classes we add. 

\(\displaystyle 12+6=18\)

Each square represents \(\displaystyle 3\) students. Ms. Smith's bar has \(\displaystyle 5\) squares in it, which means she has \(\displaystyle 15\) students with pets (\(\displaystyle 3\times5=15\)). Ms. Hen's bar has \(\displaystyle 2\) squares in it, which means she has \(\displaystyle 6\) students with pets (\(\displaystyle 3\times2=6\)). 

To find the total in both classes we add. 

\(\displaystyle 15+6=21\)

Each square represents \(\displaystyle 7\) students. The first grade bar has \(\displaystyle 4\) squares in it. That means we can take \(\displaystyle 7\times 4\) to find our total. 

\(\displaystyle 7\times4=28\)

Each square represents \(\displaystyle 7\) students. The second grade bar has \(\displaystyle 5\) squares in it. That means we can take \(\displaystyle 7\times 5\) to find our total. 

\(\displaystyle 7\times5=35\)

Each square represents \(\displaystyle 7\) students. The third grade bar has \(\displaystyle 2\) squares in it. That means we can take \(\displaystyle 7\times 2\) to find our total. 

\(\displaystyle 7\times2=14\)

Each square represents \(\displaystyle 7\) students. The first grade bar has \(\displaystyle 4\) squares in it, which means there are \(\displaystyle 28\) students who have a sibling (\(\displaystyle 7\times4=28\)).The third grade bar has \(\displaystyle 2\) squares in it, which means there are \(\displaystyle 14\) students who have a sibling (\(\displaystyle 7\times2=14\)). 

To find the difference we subtract. 

\(\displaystyle 28-14=14\)

Each square represents \(\displaystyle 7\) students. The first grade bar has \(\displaystyle 4\) squares in it, which means there are \(\displaystyle 28\) students who have a sibling (\(\displaystyle 7\times4=28\)).The fourth grade bar has \(\displaystyle 3\) squares in it, which means there are \(\displaystyle 21\) students who have a sibling (\(\displaystyle 7\times3=21\)). 

To find the difference we subtract. 

\(\displaystyle 28-21=7\)

Each square represents \(\displaystyle 7\) students. The fourth grade bar has \(\displaystyle 3\) squares in it, which means there are \(\displaystyle 21\) students who have a sibling (\(\displaystyle 7\times3=21\)).The third grade bar has \(\displaystyle 2\) squares in it, which means there are \(\displaystyle 14\) students who have a sibling (\(\displaystyle 7\times2=14\)). 

To find the difference we subtract. 

\(\displaystyle 21-14=7\)

Each square represents \(\displaystyle 7\) students. The second grade bar has \(\displaystyle 5\) squares in it, which means there are \(\displaystyle 35\) students who have a sibling (\(\displaystyle 7\times5=35\)).The third grade bar has \(\displaystyle 2\) squares in it, which means there are \(\displaystyle 14\) students who have a sibling (\(\displaystyle 7\times2=14\)).

To find the difference we subtract. 

\(\displaystyle 35-14=21\)

Each square represents \(\displaystyle 7\) students. The second grade bar has \(\displaystyle 5\) squares in it, which means there are \(\displaystyle 35\) students who have a sibling (\(\displaystyle 7\times5=35\)).The first grade bar has \(\displaystyle 4\) squares in it, which means there are \(\displaystyle 28\) students who have a sibling (\(\displaystyle 7\times4=28\)).

To find the difference we subtract. 

\(\displaystyle 35-28=7\)