Answer:
21 gallons
Step-by-step explanation:
The tank is half full after the 7 gallons goes into it. It started with 1/6 of a tank. 1/2 - 1/6 = 1/3. That means that it took 7 gallons to fill that 1/3. We can use proportions now to solve this:
[tex]\frac{gallons}{tank}:\frac{7}{\frac{1}{3} }=\frac{x}{1}[/tex]
where x is the number of gallons when the tank is full (1). Cross multiply to get:
[tex]\frac{1}{3}x=7[/tex] so
x = 21 gallons
