Question 246873
.20*15+.60x=.30(15+x)
3+.60x=4.5+.30x
.60x-.30x=4.5-3
.30x=1.5
x=1.5/.30
x=5 ml. of 60% alcohol is used. 
Proof:
.20*15+.60*5=.3(15+5)
3+3=.3*20
6=6