Answer:
27
Step-by-step explanation:
x + y = 15 (gallons) (1)
0.25*x + 0.10 * y = 0.15 * 15 (2)
Multiply 100 on (2):
25x + 10y = 15
Divede by 5
5x + 2y = 3 (3)
From (1) y = 15 - x
so 5x + 10*(15 - x) = 15
5x + 150 - 10x = 15
-5x = 15 - 150 = -135
x = 135/5 = 27 (gallons)
