Question 979285
x = full capacity of the tank (in gallons)


"Frank's gas tank was 1/4 full" so it has (1/4)*x = x/4 gallons of gas in it already.


Add on G gallons: (x/4) + G


This is equal to 7/8 of the full capacity, so (x/4) + G = (7/8)x


-------------------------------------------------------


Solve for x


(x/4) + G = (7/8)x
(x/4) + G<font color="blue">-(x/4)</font> = (7/8)x<font color="blue">-(x/4)</font>
G = (7/8 - 1/4)x
G = (7/8 - 2/8)x
G = (5/8)x
<font color="blue">(8/5)*</font>G = <font color="blue">(8/5)*</font>(5/8)x
(8/5)*G = x
x = (8/5)*G
x = 8G/5


The full capacity of the tank is <font color="red">8G/5</font>