6.40 years
Set P(t) equal to 1 million and solve for t. Logarithms make it easy.
1,000,000 = 201,753×e^(0.25t)
1,000,000/201,753 = e^(0.25t) . . . . divide by the coefficient of the exponential
ln(4.95656) = 0.25t . . . . . . take the natural log. Next, divide by the coefficient of t.
ln(4.95656)/0.25 = t ≈ 6.04
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Comment on the graph
The function graphed is the population in millions. The horizontal axis is the time in years, so the curve crosses the million mark at 6.403 years.