Question 329213
The formula for finding the area of a rectangle is A = L*W. 
Let A = x^2 + 50x 
Let L = length 
Let x = width 
x^2 + 50x = Lx 
(x^2 + 50x)/x = L 
x + 50 = L 
The binomial expression that represents the length is x + 50. 
Did you follow?