First of all, when you start an equation with a slope, since the question gave the slope -3, I'm not sure what your looking for, but I'll give you an example
Example: y-y₁ = m(x-x₁) m = -3 y₁ = ? - I'll just put a random # = -1 x₁ = ? - I'll just put a random # = 5 <span>y-(-1) = (-3)(x-(5)) </span>y+1 = -3x+15 - I'm guessing