47,628
First you want to find the area of the candle. Which you multiply base (2) times width (7) times hight (9)
2•7•9=126
Now that the area is found of one singular candle, to find out how much wax you would need for 378 candles all you have to do is multiply 126 by 378
126(378)= 47,628
47,628 cubic inches of wax is the answer.