Length of st is 16 Since p is the midpoint of st, that makes sp half of st. So sp = x+4 Given st = 4x Given st = 2(sp) length of st is twice length of sp st = 2(x+4) Set the two different ways of describing st equal to each other. 4x = 2(x + 4) Distribute the 2 4x = 2x + 8 Subtract 2x from both sides 2x = 8 Divide both sides by 2 x = 4 Now substitute the value 4 for x in the length of st st = 4x st = 4*4 st = 16.