The perimeter of a rectangular floor is 80 feet. Find the dimensions of the floor if the length is three times the width

A) 2L + 2W  = 80
B) L = 3W or L -3W =0
Multiplying Equation B) by -2
B) -2L +6W = 0  then adding equation A
A) 2L + 2W = 80
8W = 80
Width =10
Length = 30