Solve the simultaneous equations: 5x + y = 21 and x - 3y = 9

x = 4.5y = -1.5To answer this question, first, rearrange the first equation to make y the subject: 5x + y = 21 --> y = 21 - 5xYou can now substitute this value of y into the second equation: x - 3(21 - 5x) = 9Now expand out the brackets: x - 63 + 15x = 9 --> 16x - 63 = 9rearrange to make x the subject: 16x = 72 --> x = 72/16 = 4.5now we can calculate y but substituting the value for x into the first equation: 5(4.5) + y = 21--> 22.5 + y = 21rearrange for y: y = 21-22.5 = -1.5