How do you use Substitution to solve simultaneous equations?

For the equations 3x + 2y = 4 (1) and 4x + 5y = 17 (2), isolate one of the unknowns in one equation to one side, like so: 3x = 4- 2y. Next multiply the equations so that this unknown is the same in both. A good method for this is to multiply each equation by the others x number, so for our equations we multiply 1x4 and 2x3 to give 12x = 16 - 8y (1) and 12x + 15y = 51 (2). Now you need to sub one into the other using the equivalent terms you have obtained. in our example we will sub 12x = 16 - 8y into 12x + 15y = 51 to get (16 - 8y) + 15y = 51. We now have to solve the equation normally: 15y - 8y = 51 - 16 --> 7y = 35 --> y = 5. Finally, sub the value you found into one of the original equations. For this we sub y = 5 into 1 to get 3x + 2(5) = 4 --> 3x + 10 = 4 --> 3x = -6 --> x = -2.