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? Let's think first. Chain of thought:
The rectangle has a length of 1638 in / 42in = 39 in. The number of rectangles required to reach 390 inches is 390 / 39 = 10 rectangles.
Therefore, the answer is 10.