First, you want to divide both sides of the equation by 3, so we have the equation in the simplest form. Thus, we have an equation: 3x + y = 5.
Slope intercept form means the equation is in the y = mx + b form. In this case, y is y, m is 3 (coefficient of x) x is x, and b is 5. So, subtracting 3x from both sides means we have our answer of y=5-3x.
