If henry were to add 5 gallons of water to a tank that is already 34 full of water, the tank would be 78 full. how many gallons of water would the tank hold if it were full?

Please express those fractions properly:  3/4, 7/8.

Let g be the # of gallons the tank could hold when full.  

Then (3/4)n + 5 = (7/8)n.  

solving for n:  Mult all 3 terms by the LCD (8):  6n + 5(8) = 7n.

Then n=5(8) = 40 (gallons).  The tank would hold 40 gallons of water were it full.

The answer is 76° i believe