Answer:
18 mins
Step-by-step explanation:
if 12mins is 40%
then add 12mins again
12+12=24
so 24 is 80%
then divide 12 by 2 and add it to 24
12/2=6
24+6=30
eleanor practiced 30 mins with his violin per day
he has practiced 12 mins out of 30mins
so he has 18 mins more to practice