Question 1028691
Income = (5 + 0.50x)(400 - 8x), where x = number of increment times.

==> Income = 4(10 + x)(50 - x), after factoring.

==> The roots are x = -10, 50.
The maximum is attained at the midpoint of -10 and 50, namely x = 20.

==> The fare should be $15 in order to maximize income, and the maximum income is $3,600.