Question 138985
The basic formula is {{{d=rt}}}, distance equals rate times time.


Let Chuck's rate be {{{r[c]}}} and Dana's rate be {{{r[d]}}}.


Chuck traveled 93 miles at a rate of {{{r[c]}}} for some time {{{t}}}


Dana traveled 84 miles at a rate of {{{r[d]}}} for the SAME time {{{t}}}


If we rearrange the basic formula so that it is solved for time we get {{{t=d/r}}}


So, Chuck's trip took {{{t=93/r[c]}}} hours, and Dana's trip took {{{t=84/r[d]}}} hours.  But the time was the same for both trips, so we can say:


{{{84/r[d]=93/r[c]}}}


We are also told that Chuck's rate is 3 mph greater than Dana's, so {{{r[d]=r[c]-3}}}, and we can substitute this fact into the last equation, thus:


{{{84/(r[c]-3)=93/r[c]}}}


Now all you have to do is solve this equation for {{{r[c]}}} to get Chuck's speed.  HINT: Cross multiply this proportion and then collect like terms