Question

The Randolph’s used 12 more gal of fuel oil in October than in September and twice as much oil in November as in September. If they used 132 gal for 3 months, how much was used during each month?

Let the usage in the three months be S, O and N.
O = S + 12
N = 2S
S+O+N = S + S + 12 + 2S= 132
3S = 120
Solve for S.
The use the O and N equations to get the others.