Question 26209
Let x = second side
Let 2x+8 = first side
Let 3x = third side

the perimeter is the addition of all three sides so:

x+2x+8+3x = 128
add the like terms:
6x+8 = 128
subtract 8 from both sides of the equation:
6x=120
divide both sides by 6 to get:
x=20

Hope you understand!