I don't like algebra masquerading as geometry. Algebra and geometry are connected in interesting ways, but this is boring.
It just says the two little angles add to the big angle,
(2x + 6) + (10x - 5) = 73
Solving,
12x + 1 = 73
12x = 72
x = 6
SQR = 2x+6 = 18 degrees
PQR = 10x -5 = 55 degrees
