Find (f+g)(x) and (f-g)(x) for f(x)=6x^2+5 and g(x)=7-5x

Keshawn needs to enclose a pen for her pigs. she only has 200 feet of fencing and wants to enclose the maximum area. she sets up the equation a = l(100-l) to find what the length of the pen should be. what does 100 - l represent? a) the width of the pen b) the length of the pen c) the area of the pen. d) the perimeter of the pen