Answer:
Step-by-step explanation:
In similar triangles, corresponding sides are in same ratio
Cross multiply,
7*(x + 8) = 6*(3x -9 )
7x + 7*8 = 6*3x - 6*9
7x + 56 = 18x - 54
56 = 18x - 7x -54
56 = 11x - 54
11x - 54 = 56
11x = 56 +54
11x = 110
x = 110 /11
x = 10
PR = 3x -9
= 30 - 9
PR = 21