What happens to the slope when a line with positive slope gets close to vertical

1jessica's home town is a mid-sized city experiencing a decline in population. the following graph models the estimated population if the decline continues at the same rate. select the most appropriate unit for the measure of time that the graph represents. a. years b. hours c. days d. weeks

Rose bought a new hat when she was on vacation. the following formula describes the percent sales tax rose paid b=t-c/c

Having a hard time understanding this question (see attachment).