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

Two equations 1) 5x + y = 21, 2) x - 3y = 9. Eliminate x or y by manipulating equations 1 or 2. Equation 3 = equation 2 x 5 = 5(x-3y) = 5(9) 3) 5x - 15y = 45. Equations 3 & 1 both have 5x's so we can subtract equation 1 from equation 3 to get a new equation with only y's, no x's.(5 - 5)x + (-15 - 1)y = 45 - 21, which evaluates to -16y = 24, giving y = -24/16 = -3/2 = -1.5. This value of y satisfies equations 1 & 2. Substitute this value into 1 or 2 to find x: 5x + (-1.5) = 21, 5x = 21 - -1.5 = 22.5, x = 4.5. So x = 4.5 & y = -1.5 are solutions to the pair of simultaneous equations.