How many gallons of 30% antifreeze should be mixed with 10 gallons of 93% antifreeze to obtain a 65% antifreeze mixture?

The answer to this question is 9.9

0.3*x+0.75*10=0.55 (10+x)

0.3*x+7.5=5.5+0.55x

0.3x-0.55x=5.5-7.5

-0.25x=-2

x=8 liters at 30% is added to 10 liters of 75% to get 18 liters at 55%

NOW! Let; s check if it's the right answer

0.3*8+0.75*10=0.55 (10+8)

2.4+7.5=0.55 (18)

9.9=9.9