Glencoe Algebra 2, Chapter 2, 2.4, Section 2.4, Problem 23

We can do this in one shot by using the point slope form instead, y-y1=m (x-x1) and simply solve for y.
The slope, m, is 3
The (x1,y1) is (0,-6)
y-y1=m (x-x1)
y-(-6)=3 (x-0)
y+6=3×-0
y+6=3x
y=3x-6