The height of a cone is equal to the diameter of the base. what expression represents the volume of the cone, in cubic units?

By definition, the volume of a cone is given by:
 
 Where,
 r: radius of the circular base
 h: height of the cone
 Let's define a variable:
 x: diameter of the base
 We have then that the radio is:
 
 The height is:
 
 Substituting values:
 
 Rewriting:
 
 
 An expression that represents the volume of the cone, in cubic units is:
 

This makes absolutely no sense at all young man/women

It’s 24.6 after you round to the nearest tenths the answer should be 25.0