This is a semi-log plot so
y = c ekx
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 m2 then k must have units m-2
k = 0.031 m-2

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