Question 702873
x is length.  w is width.

Three times as long as it is wide:  x=3w

Perimeter is 144:  144=2x+2w



Easiest way is substitute x from first equation into the second equation.
144=2(3w)+2w
144=8w
w=144/8=72/4=36/2=18.

w=18 means x=3(18)=36