The earnings function is given by $c=300,000+125,000 t$. We integrate this from 0 to 3 (the duration of the contract in years) to get the total earnings over the three years.
\[
\int_{0}^{3} (300,000+125,000t) dt = [300,000t + \frac{125,000}{2}t^2]_{0}^{3}
\]
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