Answer:
20 grams
Step-by-step explanation:
Let g represent the grams of solution that were replaced. Then the amount of alcohol in the mix is ...
16%·(120 -g) +100%·g = 30%·120
19.2 +0.84g = 36.0 . . . . simplify
0.84g = 16.8 . . . . . . . . . .subtract 19.2
g = 20 . . . . . . . . . . . . . . .divide by 0.84
20 grams of solution were taken out and replaced.