Answer:
B 7
Step-by-step explanation:
Since the triangles are similar by AAA
We can use ratios to find the length x (which is PR)
5 15
-------- = ------------
x 21
Using cross products
5 * 21 = 15 *x
Divide each side by 15
5/15 * 21 = 15x/15
1/3 * 21 =x
7 =x
