To find out when the two popcorn machines will have the same amount of popcorn left, we can represent the amount of popcorn left in each machine after \( x \) hours.
For Movie Theater A:
- Initial capacity: 120 gallons
- Popcorn sold per hour: 7 gallons
- Amount left after \( x \) hours: \( 120 - 7x \)
For Movie Theater B:
- Initial capacity: 150 gallons
- Popcorn sold per hour: 9 gallons
- Amount left after \( x \) hours: \( 150 - 9x \)
We want to find \( x \) when the amounts left in both machines are equal: \[ 120 - 7x = 150 - 9x \]
Now, let's solve for \( x \):
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Rearrange the equation: \[ 120 - 7x + 9x = 150 \] \[ 120 + 2x = 150 \]
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Subtract 120 from both sides: \[ 2x = 30 \]
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Divide by 2: \[ x = 15 \]
Therefore, the correct equation that shows when the two popcorn machines will have the same amount of popcorn left is option d: \[ 120 - 7x = 150 - 9x ; ; ; x = 15 \]