The domain of any polynomial is
.. all real numbers.
First, list all the given information:
*100 miles/week
*25 miles/gallon
*$4/gallon
*weekly expenditure reduced by $5
The easiest approach to use here is the dimensional analysis. Cancel out like units if they appear both in the numerator and denominator side. Solve first the original cost. The solution is as follows:
100 miles/week * 1 gal/25 miles * $4/gal = $16/week
The reduced cost would be:
16 - 5 = (New average miles/week) * 1 gal/25 miles * $4/gal
New average miles/week = 68.75 miles/week
