To solve by substitution, you need to fill in the value for either x or y. Since y = x + 5, you already have the y value. It's x + 5. Now you need to find x before you can go any further. So let's take 5x + y = 3 and fill x + 5 in for y. 5x + y = 5 5x + x + 5 = 3 Now solve for x. 5x + x + 5 = 3 6x + 5 = 3 6x = 3 - 5 6x = -2 x = -2/6 or -0.33 Now solve x + 5 for y. y = x + 5 y = -0.33 + 5 y = 4.67 So x = -0.33 and y = 4.67