Question 1143964
The cost of a taxi ride is given by C=rd+a, where r is the rate per one-fifth mile, d is the trip distance in terms of the number of one-fifth-mile units in the trip, and a is the flag-drop fee (an automatic charge created when the meter is started).
 Solve the equation for the mileage rate r. 
write it:
rd + a =  C
rd = C - a
divide both sides by d
r = {{{((C-a))/d}}}, (rate is per 1/5 mile)