Step-by-step explanation:
so let's say that the width is x then the length is x+15
and the area of a square is length times width
x(x+15)=100
x^2+15x-100=0
(x+20)(x-5)=0
x=5 or x=-20 but a side length can't be negative so x would equal 5
Length=x+15 with 5 as x
Length=20
Width=5
Hope that helps :)