The whooping crane (Grus americana) is the tallest bird native to North America. It almost went extinct in the 1900s; in 1938, there were only 18 whooping cranes left in the wild. Since then, its population has increased. The number of whooping cranes (N) is related to the number of decades since 1938 (t) by the following expression: ln(N) = 2.85 + 0.039t. The exponential relationship can be written as N = nakt, where n, a, and k are constants. Determine the value of a.