Do you have a rectangular prism?
Because if the dimensions you given are the length width and height, just multiply them all together:
8 • 14 • 18 = 2,016
FINAL ANSWER:
2,016 square meters
KEEP IN MIND THIS IS ONLY IF THE FIGURE YOU HAVE IS A RECTANGULAR PRISM
IF YOU DONT LEAVE THIS ALONE
Comm.ent me if u have any questions
-SpaceMarsh