Math problem help please?

Let V gallons be the volume of the 25% alcohol solution.
Then, the volume of the 45% alcohol solution = (12 - V) gallons

Volume of alcohol in the final 12 gallons of solution :
V × 25% + (12 - V) × 45% = 12 × 30%
0.25V + 5.4 - 0.45V = 3.6
0.2V = 1.8
V = 9
12 - V = 3

There needs to be ___9___ gallons of 25% alcohol solution, and ___3___ gallons of 45% of alcohol solution.

30% × 12 gal = 3.6 gal
12 gallons of 30% solution contain 3.6 gallons of pure alcohol.

Let x be the number of gallons of 25% solution used to make the 30% solution. Then (12-x) is the number of gallons of 45% solution used.
x gallons of 25% solution contain 0.25x gallons of pure alcohol
(12-x) gallons of 45% solution contain (5.4-0.45x) gallons of pure alcohol
0.25x + (5.4-0.45x) = 3.6
1.8 = 0.2x
x = 9
12-x = 3

Use 9 gallons of 25% solution and 3 gallons of 45% solution to make 12 gallons of 30% solution.

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