What is the volume ?? Please I need help

What is the difference between the equations of a vertical and a horizontal line?

Asales representative from a local radio station is trying to convince the owner of a small fitness club to advertise on her station. the representative says that if the owner begins advertising on the station today, the club's total number of members will grow exponentially each month. she uses the given expression to model the number of club members, in hundreds, after advertising for t months.

What is the domain of the step function f(x)=[2x]-1?