Hi there
The rule of 72 is
72/rate=time
72÷3=24 years
Hope it helps
Answer: 
<u>Move all terms to the left</u>
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<u>Add all the numbers together, and all the variables</u>
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<u>Multiply elements</u>
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<u>Move all terms containing d to the left, all other terms to the right</u>
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Answer:
<u>C. 90</u>
Step-by-step explanation: