You can
put this solution on YOUR website!the let is correct
"A side of a square is 10 meters longer than the side of an equilateral triangle" __ x+10
"The perimeter of the square is 3 times the perimeter of the triangle" __ 4(x+10)=3(3x)
4x+40=9x __ subtracting 4x __ 40=5x __ 8=x