a = amount of solution A used
b = amount of solution B used
a + b = 330 (mL, not mm)
Each mL of x% alcohol solution contributes x/100 mL of alcohol; in order to end up with a mixture that is pure alcohol, all 330 mL of the mix needs to be alcohol:
0.12a + 0.19b = 330
Deandre uses 3 times as much of solution A as he does of solution B, so that
3a = b
in which case
a + 3a = 330 ==> 4a = 330 ==> a = 82.5 ==> b = 247.5
But
0.12a + 0.19b = 56.925 ≠ 330
