The cost, C, to produce b baseball bats per day is modeled by the function C(b) = 0.06b2 – 7.2b + 390. What number of bats should be produced to keep costs at a minimum?

The cost function is a quadratic that opens upward because the coefficient of b² is positive (0.06), so its minimum occurs at the vertex. The vertex’s b-value is −(−7.2) ÷ (2 × 0.06) = 7.2 ÷ 0.12 = 60. Therefore, costs are minimized by producing 60 bats per day, choice B.

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