Question

The gasoline gauge on a van initially read 1/3full. When 10 gallons were added to the​ tank, the gauge read 3/4 full. How many more gallons are needed to fill the​ tank?

Answer 1

the tank went from 1/3 full, to 3/4 full, and upper level
and that happened after 10 gallons were added
meaning, if the tank  is full at "x"

the difference between 3/4x and 1/3x is 10
thus $\bf \cfrac{3x}{4}-\cfrac{1x}{3}=10$

solve for "x"