A company makes wax candles in the shape of a rectangular prism. Each candle is 5 inches long, 3 inches wide, 7 inches tall, inches tall. How much wax will they need to make 420 candles?
The volume of each candle is given by the formula V = lwh, where l is the length, w is the width, and h is the height.
So, V = 5 inches x 3 inches x 7 inches = 105 cubic inches.
Therefore, they will need a total of 105 cubic inches x 420 candles = <<105*420=44100>>44,100 cubic inches of wax. Answer: \boxed{44100}.