a) Runner's pulse at the end of the race? t=0.

The runner's pulse at the end of the race is 145 beats per minute.

a) Runner's pulse 1 minute after the end of the race? t=1.

The runner's pulse 1 minute after the end of the race is approximately 132 beats per minute.

b) How long after the end of the race will the runner's pulse be 80 beats per minute?

To the nearest minute, the runner's pulse will be 80 beats per minute after 6 minutes.

or*

* note the disagreement between the two approximations, supplied by the same calculator.