If uvw ~ rst ,what is the value of x?

x = 15

Step-by-step explanation:

Since the triangles are similar, we can say that the ratio between the respective sides of the first triangle and the 2nd is constant.

Basically, VW / ST = VU/SR = WU/TR = k, where k is a positive real number

Solving for k is simple:

k = VU/SR = 42/21 = 2

So we found out that the 1st triangle is the 2nd triangle but scaled up 2 times.

We use this to find x.

ST * 2 = VW

2x = 30

x = 15