Question

Hello there again!
A school is sending 15 children to a camp. If 30% of the children in the school are first graders, and the 15 children are selected at random from among all 6 grades at the school, find the mean and the variance of the number of first graders chosen.

I was able to get the mean which is 4.5, but i am having problems finding the variance..... The answers i have are narrowed between two options
a.
The mean is 4.5 and the variance is 3.2
c.
The mean is 4.5 and the variance is 1.8