Question 40996
You are correct:

Area of the triangular sail is:
{{{A = bh/2}}}

A is given as: {{{x^2+5x+6}}}  and h is given as: {{{x+3}}}, making the appropriate substitutions, you get:

{{{x^2+5x+6 = b(x+3)/2}}} Solving this for b, you get:
{{{b = (2x^2+10x+12)/(x+3)}}} You can simplify this by dividing or by factoring & canceling...the latter is easier.

{{{b = (2x+4)(x+3)/(x+3)}}} Cancel the (x+3)'s
{{{b = 2x+4}}} which is exactly what you got!