What is teh slope equation of (4,-6) and m=3?

For all slope equations, their general form is always y=mx +c (always), where m is the gradient, in this case, it's 3.
Take y-coordinate and x- coordinate from (4,-6) and pluck it into the equation.
-6 = (3)(4)+c where c is unknown to us
-6 = 12 + c
c =-18
so the slope equation is y=3x-18