I assume the questioner wants me to find S and not x. If he insist, x, then the answer is 0 because there's no such variable x in the question. On the other hand finding S. We have QS = 42 Hence S = 42/Q. Substituting into the second eqn we have Q (42/Q) = QR + R (42/Q); so we have 42 = QR + 42R/Q.
