Please help urgently!! I’m stuck

Show algebraically that f and g are inverse functions f(x)=x^2/-6; g(x)=square root of 2x+12

Each of the walls of a room with square dimensions has been built with two pieces of sheetrock, a smaller one and a larger one. the length of all the smaller ones is the same and is stored in the variable small. similarly, the length of all the larger ones is the same and is stored in the variable large. write a single expression whose value is the total area of this room. do not use any method invocations.

If you answer 2+2 you will get over 80 points