When finding zeros, the function has to equal zero. In other words, G(x) = 0.
For three multiplied parts to equal to zero, at least one has to be zero. -2 ≠ 0, but (x+1) or (x+7) can.
So you can equate each of those to zero and find out what the zeros are.
x+1=0
x=-1
x+7=0
x=-7
Thus the answer
x = -1 or -7