Question

Please help 25 points problem below

Answer 1

b - the base

h = b + 3 - the height

The formula of an area of a triangle:

$A=\dfrac{1}{2}bh$

Substitute:

$A(b)=\dfrac{1}{2}b(b+3)=\dfrac{1}{2}(b^2+3b)\to\boxed{A.}$