Assuming the chest is a rectangular prism, the volume formula is just length(width)(height), or y = lwh
The final volume is 8,100 inches, which can replace the y. The length is 30 inches, which can replace the l. The width is 15 inches, which can replace the w. Now all you have to do is fill in the blanks and solve.
8,100 = h(15)(30)
8,100 = h(450)
8,100 / 450 = h
18 = h
It will be 18 inches tall.
