Question 660358
b + y = 12
7b = y

Substitution
b + 7b = 12
8b = 12
b = 12/8
b = 1 4/8 or 1 1/2 gallons

y = 7(12/8)
y = 84/8 
y = 10 4/8 or 10 1/2 gallons