I guess by slope, you mean gradient.
By knowing the gradient, and a coordinate at which the line passes through, we can use:
y - y1 = m(x - x1)
to get the equation of the line in the form (y = mx + c).
y - 5 = (-3 / 4)(x - 4)
y - 5 = (-3 / 4)x + 3
Rearrange.
y = (-3 / 4)x + 8
