Explanation:
Using stratified random sampling, researchers must identify characteristics, divide the population into strata, and proportionally choose individuals for the representative sample. ... For example, individuals who are too busy to participate will be under-represented in the representative sample.
I know for number 4 the answer is c, sorry I can't help with the others.
Volume well in the picture the fish tank seems to be a rectangle, so you would do V=length x width x height. So V=5x3x3=45