let

l = the length of the window

w = the width of the window

the perimeter of a rectangular window is 26 feet

2(l + w) = 26 divide both sides by 2

l + w = 13

the width of the window is 5 feet greater than the length

w = l + 5

by solving the system of equations:

l + w = 13

w = l + 5

we find

l = 4 ft

w = 9 ft

click here to see the step by step solution of the system of equations

the dimensions of the window are 4 ft and 9 ft.