What is the geometric mean of 21 and 54?

Adam plans to choose a video game from the section of the store where everything is 75% off. he writes the expression d-0.75d to find the sale price of the game if the original price is d dollars. gena correctly writes another expression, 0.25d, that will also find the sale price of the game if the original price is d dollars. use the drop down menus to explain each part of adams and rena's expression

How do i do this activity, is appreciated

F(x) = 1/x g(x)=x-4 can you evaluate (g*f)(0) ? why or why not?