Let's analyze the problem step by step.
We want to find out when the amount of popcorn left in both machines will be the same. We'll denote \( x \) as the number of hours that pass.
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The amount of popcorn left in Theatre A after \( x \) hours: \[ \text{Remaining popcorn in A} = 120 - 7x \]
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The amount of popcorn left in Theatre B after \( x \) hours: \[ \text{Remaining popcorn in B} = 150 - 9x \]
Next, we set these two expressions equal to each other to find out when the amounts are the same: \[ 120 - 7x = 150 - 9x \]
Now, let's solve this equation for \( x \).
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Start by rearranging the equation: \[ 120 - 7x = 150 - 9x \]
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Add \( 9x \) to both sides: \[ 120 + 2x = 150 \]
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Now, subtract \( 120 \) from both sides: \[ 2x = 30 \]
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Finally, divide by \( 2 \) to solve for \( x \): \[ x = 15 \]
Thus, the two popcorn machines will have the same amount of popcorn left after 15 hours.
So the correct equation from the options provided is:
Correct Option:
- 120 - 7x = 150 - 9x ; x = 15