Question 838510
The distance is the same both ways, both days.


_____________speed_________time__________distance
Thursday_____r_____________3.6___________d
Friday_______r-4___________4_____________d


That's one way to arrange the data.  The question is, "speed on friday".  We can reassign the rate variable like this:

_____________speed_________time__________distance
Thursday_____r+4___________3.6___________d
Friday________r____________4_____________d

The rate on Friday is still 4 mph slower than thursday, so this data arrangement should still work.



RT=D, typical meanings, so we should understand adding this information:

_____________speed_________time__________distance
Thursday_____r+4___________3.6___________d=(r+4)(3.6)
Friday________r____________4_____________d=r*4


All needed is to solve for r in {{{(r+4)(3.6)=r*4}}}, rewritten as {{{highlight((3.6)(r+4)=4r)}}}