Remember, when adding or subtracting, the answer uses the least number of decimal places. 1542 has the least number of decimal places (numbers after a decimal) because it has none. So the answer just needs to lack any decimal places.

When multiplying or dividing, the answer uses the least number of significant figures of the given values. 12 had the least number of significant figures (2), so the answer must have 2 significant figures as well.

Remember: when multiply or dividing, the answer uses the least number of significant figures of the given values. Here, 45.51 has the least number of significant figures (4), which is why the answer must also have 4 significant figures.

When dealing with decimal numbers, zeros only count as long as there is a non-zero number somewhere before them. The first 4 zeros have no non-zero number before them, so they don't count as significant figures. The last 2 zeros have a 5 in front of them, so those zeros count as significant figures, and so does that 5; which gives us a total of 3 significant figures.

For scientific notation, the exponent next to the ten has nothing to do with significant figures; it's the decimal number before it that determines the number of significant figures. Based on those decimal numbers, $\displaystyle 2\cdot 10^3$  and $\displaystyle 4\cdot 10^3$ each have one significant figure, and $\displaystyle 8.11\cdot10^4$ has three significant figures. When dealing with non-decimal numbers, zeros only count if they are in between two non-zero numbers. That means that 1,340 only has three significant figures, and 1,001 has 4 significant figures.

Whenever multiplying, the final answer will have the same number of significant figures as the number with the least least number of significant figures in the question. 130.5 has 4 significant figures and 12 has 2 significant figures, that means that our answer must have 2 significant figures. $\displaystyle 130.5 \cdot 12 =1566$, but that's 4 significant figures instead of 2. So we need to round this to 2 significant figures. Our answer to the correct number of significant figures is 1600.

When adding numbers, the answer should use the the least number of decimal places of those in the question. 14.1 has one decimal place (one number behind the decimal), 12 has no decimal places, and 5.634 has 3 decimal places; this means that the answer must have no decimal places. $\displaystyle 14.1 + 12 + 5.634 =31.734$, this must be rounded to zero decimal places. Thus we round up to 32.

Notice that the most precise you can get with your volume measurement is $\displaystyle \pm0.1\,mL$ and your recorded value has 3 significant figures. You must take no more than 3 significant figures for your pressure measurement even if the device is more precise than this (which it is). Your recorded value must be

$\displaystyle 102\,kPa$