Question 1107327
R, fuel efficiency, miles per gallon
P, price, dollars per gallon

D, given number of miles distance

{{{D(1/R)}}}--------how many gallons


{{{D(1/R)P}}}--------the cost for going distance D.


{{{highlight_green((DP)/R)}}}-------slightly rewritten, the cost to go distance D.


ABOUT How much cost to go 75 miles, 
given r is from 22 to 28
and
p is from 3.75 to 3.95
-
{{{d(p/r)}}}

{{{system(75(3.75/28) , to ,  75(3.95/22))}}}
and you probably want the middle of these.