-21 - 9g = -3g
9g is subtracting on the left, then it will add on the right
-21 = -3g + 9g
-21 = 6g
6 is multiplying on the right, then it will divide on the left
-21/6 = g
-7/2 = g
Finally,
4g = 4*(-7/2) = -14
