Answer:
We can't solve this problem if there is no context given. Since nothing is mentioned, it is safe to assume that PR and QR are line segments. Based on the nomenclature, it may be a collinear system of 3 points: P, Q and R. The equation should be:
PR = PQ + QR
Assume x is referred to line PQ
(9x - 31) = x + 43
9x - x = 43 + 31 = 74
8x = 74
x = 9.25