
Kris V. answered 05/23/17
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Let x be the number of increases in $5 increments, then
180 + 5x is the yearly fee associated with the x increments.
1000 - 10x is the number of members associated with the x increments.
Revenue = Fee x Number of members
R(x) = (180 + 5x)(1000 - 10x) = -50(x+36)(x-100) = -50(x2 - 64x - 3600) = -50(x-32)2 + 231,200
This is the quadratic equation of a parabola which opens downward, so the maximum revenue is at the vertex of R(x).
The new fee is 180 +5(32) = $340.
Note:
The new revenue is 231,200. Compare this with the revenue for x = 0, you should get the current revenue of $180,000.