Answer:
3
Step-by-step explanation:
Darian's plans are 3 feet long, and they're for a table 9 feet long. The scale factor is 9/3 = 3. That is, he must multiply the plan size by 3 to get the actual size.
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A scale factor is usually expressed as a fraction: (model size)/(real size). Here, it looks like you want a dilation factor that is (real size)/(model size).