A unit fraction is a fraction whose numerator is 1.
Answer:
D is the answer I think......
You get everything you need from factoring the last expression:

The left side is a difference of squares, and we get another difference of squares upon factoring. We end up with

Plug in everything you know and solve for
:

A is the answer because remember A is for adults and C is for Children.
I disagree with the student because the slope is the rate of change. The slope would be 10 because the rocks are increasing by 10 every month.