Combine studied function types arithmetically to build models.
Write and interpret a combined function model from a context
Problem
A cost has base fee \(40\), a charge of \(\$0.12~\text{for}~\text{each}~\text{unit}~\text{of}~\text{speed}~s\), and fuel surcharge \(15/s\). Write the combined cost model and its sensible domain.
Big Picture
What this problem is really about
Translate the story one charge at a time before combining anything: identify the constant contribution, the quantity that grows with speed, and the quantity divided by speed. Because each piece is measured in dollars, they contribute additively to one total. Finally, let both the reciprocal denominator and the physical meaning of speed determine the sensible domain.
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