The rectangle has a length of 1638 in/ 42in = <<1638/42=39>>39 in.

The number of rectangles required to reach 390 inches is 390/39 = <<390/39=10>>10 rectangles.

# Answer

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<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If a rectangle has a width of 42 inches and an area of 1638, how many rectangles of the same size would reach a length of 390 inches?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
10
If a rectangle has a width of 42 inches and an area of 1638, how many rectangles of the same size would reach a length of 390 inches?
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