lily's father used 6/10 of a full tank of gasoline on their car trip 9 gallons were used about how many gallons does the tank hold?

To find out how many gallons the tank holds, we can set up a proportion:

6/10 (fraction of tank used) = 9 gallons (amount used)
x (total tank capacity) = ?

Cross multiply to solve for x:
6/10 * x = 9
6x = 9 * 10
6x = 90
x = 90 / 6
x = 15

Therefore, the tank holds 15 gallons of gasoline.