The answer is B. $1600 because you have to subtract it
I think the answer is x equals 21
They didn't distribute the 3 before doing the addition in the second step. They should've added 15 to both sides because 3*5 = 15
F(3) occurs when x =3. So lets plug 3 into our equation.
F(3) = -28
I hope this helps! :)