In a certain office tower the ground level is indicated by 0, and the underground levels are indicated by –1, –2, –3, and so on. The above ground levels are indicated by 1, 2, 3, and so on.a) Andy was at Level –1 and took the elevator to Level 21. How many levels did the elevator move upward?b) Kate works on Level 12 and parks her car on the lowest level. If she has to travel 16 levels down to get her car, how many underground levels are in the office tower?