y = c e

ln y = ln c + kx

Therefore a semi-log plot gives a straight line.

In the graph c is the intercept so c = 20 s.

The slope of the graph is k. Using the points (45,80) and (0,20)

Find the units of k:

The quantity kx must be dimensionless (since it appears as an exponent).

Since x has units m

k = 0.031 m