When you are substituting equations, all you are doing is plugging in variables. Lets do an example..something random but easy... y = 2x - 3 4x + 2y = 10 So since 2x + 3 equals y we are going to plug in those numbers into the second equation. 4x + 2(2x - 3) = 10 Now we distribute 4x + 4x - 6 = 10 Combine like terms. 8x - 6 = 10 Add 6 to both sides. 8x = 16 Divide. x = 2 And thats how you substitute equations. I hope this helps love! :)