Answer: The width is 37 feet
Given data
Volume = 10, 878 cubic feet
Length = 7 feet
Height = 42 feet
width = ?
Let width = w
Volume of the rectangular prism = l x w x h
10, 878 = 7 x 42 x w
10, 878 = 294 x w
10, 878 = 294w
Divide both sides by 294
10, 878 /294 = 294w/294
w = 10, 878 / 294
w = 37 feet
Therefore, the width is 37 feet