Heres 2 photos idk showed but does anyone know the answer?

Which problem could be  solved  by evaluating the expression  7×(−3)7×-3?

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

The birth weights of newborn babies in the unites states follow in a normal distrubution with a mean of 3.4 kg and standard deviation of 0.6 kg. reaserches interested in studying how. children gain weights decide to take random samples of 100 newborn babies and calculate the sample mean birth weights for each sample