I skipped geometry and moved to alg 2 from alg 1, long story. Anyway problem is:

The formula for the area A of a circle with diameter d is A=pi(d/2)squared. Write an expression to represent the area of the circle.

Also there is image of a circle to the right, i'm not sure if it's significant in any way, it shows circle, diameter line, dot in middle, and (y+5) over dot.

Can somebody please explain in detail how i understand/do these?