Question 1001317
RV=D  relates fuel efficiency ( a rate ) with fuel volume and distance.  This is a basic uniform rates situation.


If variables are c for miles in city driving, and h for miles in highway driving then you may arrange rv=c  for city driving at rate r, and Rv=h  for highway driving at rate R.


DATA TABLE USING VALUES DESCRIBED AND VARIABLES STILL NEEDED
<pre>
             rate         volume(gallons)       distance (miles)
HIGHWAY      26              h/26                     h
CITY         18              c/18                     c
Total                         22
</pre>
This gives a formula for volume of fuel used if h and c are both known.
{{{h/26+c/18=22}}}




Question (b):
<pre>
              rate           volume           distance
HWY            26             h/26              h
CTY            18             90/18              90
Total                          22              480
</pre>
Make the obvious equations and see if they make sense together or what more the results mean.

{{{h/26+90/18=22}}}
{{{h/26+5=22}}}
{{{h/26=17}}}
{{{h=17*26}}}
{{{highlight_green(h=442)}}}--------the amount of highway distance possible.  If you look at the sum {{{h+90}}}, as if {{{h+90>=480}}}.  Is it true or not?
-
{{{442+90>=480}}}
{{{532>=480}}}---------certainly this is true. 


Enough fuel, yes, for the 480 mile trip which includes 90 miles in the city.