What is the value of a if the lines 2y - 2a = 6x and y + 1 = (a + 6)x are parallel?
\(2y-2a=6x\\ y = 3x+a\)
\(y+1=(a+6)x\\ y = (a+6)x-1\)
\(\text{The two lines are parallel so they have the same slope}\\ 3=(a+6)\\ a=-3\)