Question 719019
The first pieces of data give {{{18=k/78}}}.  The second piece of data gives {{{r=k/40}}} for some unknown fuel rate of r.  That altogether then is two equations and two unknowns, and as arranged, seems solvable.


Simple substitution and then simplification will do.
From {{{18=k/78}}}, get {{{k=18*78}}}
{{{highlight(r=(18*78)/40)}}}=11.7 or 12 miles per gallon