S + C = 66750 (1) (for the Store and College) S = 3*C + 1150 (2) You can rewrite these two equations in standard form S + C = 66750 (1) S - 3*C = 1150 (2) Now subtract equation (1) from equation (2). You will get -4*c = 1150 - 66750, or 4C = 66750 - 1150 4C = 65600 ==============> C = 65600/4 = 16400. ANSWER. The earning for the college is $16400. The rest 66750 - 16400 = 50350 dollars is the earning for the store. CHECK. 3*C + 1150 = 3*16400 + 1150 = 50350. ! Precisely correct !