To find when the two popcorn machines will have the same amount of popcorn left, we can set up an equation based on their capacities and sales rates.
Let \( x \) be the number of hours after which we are measuring the amount of popcorn left.
For Movie Theatre A:
- Initial popcorn: 120 gallons
- Popcorn sold: 7 gallons per hour
- Amount left after \( x \) hours: \( 120 - 7x \)
For Movie Theatre B:
- Initial popcorn: 150 gallons
- Popcorn sold: 9 gallons per hour
- Amount left after \( x \) hours: \( 150 - 9x \)
Now we can set the two expressions equal to each other:
\[ 120 - 7x = 150 - 9x \]
Now, we will solve for \( x \):
- Start by adding \( 9x \) to both sides:
\[ 120 - 7x + 9x = 150 \]
- This simplifies to:
\[ 120 + 2x = 150 \]
- Next, subtract 120 from both sides:
\[ 2x = 30 \]
- Finally, divide by 2:
\[ x = 15 \]
Thus, the solution to the equation is \( x = 15 \).
This means that in 15 hours, both popcorn machines will have the same amount of popcorn left.