Each Tuesday, a bus makes its first stop at Gauss Public Library at 1 pm. It continues to stop at the library every 20 minutes. Its last stop is at 6 pm. What is the total number of times that the bus stops at Gauss Public Library on a Tuesday.

The bus stops at the library at 1:00 p.m., 1:20 p.m., and 1:40 p.m..
The bus stops at the library at 2:00 p.m., 2:20 p.m., and 2:40 p.m..
Similarly, the bus will stop at those same three times past each hour.
So over the 5 hours, it will stop 5 × 3 = 15 times, with an additional final stop at 6:00 p.m., making a total of 15 + 1 = 16 stops.

Answer is 16 stops