Question 331989
you are actually missing two pieces of information:  $/gallon and Miles/day

if you take the information you give

{{{ 1 gallon/5 miles }}} you need to multiply this by terms in such a way
that all the terms cancel out and leave you with the terms you want ( dollars/day)

{{{ (1 gallon/5 miles) *(X miles/1 day) * (Y dollars/1 gallon)= (X*Y/5)* (cross(gallon)/cross(miles)) * (cross(miles)/day) * (dollars/cross(gallon))}}} 

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so you need to provide the X and Y unknowns