2/3 is 6/9 so 2/9 was poured out...
if 4 gallons is 2/9ths it would be
4*2+2
8+2
10gallons
X cannot equal +2, and can't be -1. If you factor it, then you notice you get 2(x+2)(x-2). If you use either one for the x, one will be zero and the won't, and vise-versa.
