Answer:
SU = 70
Step-by-step explanation:
First, we need to find the value of x. Since M is the midpoint of SU, that means that SM = MU, therefore:
x + 15 = 4x - 45
15 = 3x - 45
60 = 3x
x = 20
We know that SU = SM + MU = (x + 15) + (4x - 45) = 5x - 30 and that x = 20 so SU = 5x - 30 = 5 * 20 - 30 = 100 - 30 = 70.
