Let one piece of the rope be x
Let the other piece of rope be x + 5
These two pieces put together will make 20 feet.
So we say:
x + (x +5) = 20
What is x? We expand the equation.
x + x + 5 = 20
x + x = 20 - 5
2x = 15
x = 7.5
The shorter piece is therefore 7.5 feet.
The longer piece is 7.5 + 5 = 12.5 feet.