Question 847811
Uniform Rates Travel Equation, {{{R*T=d}}}, the rates being kilometers per hour.


Let t = "some time later", a quantity of time (not a time point).
Let d = the distance when they traveled when Rob meets Josh.


________________speed___________time___________distance
Josh____________40______________t+4__________{{{d=40(t+4)}}}
Rob_____________50______________4____________{{{d=50*4}}}


Equate the two expressions for d.  Solve for t.
Note that they "meet" when Josh traveled for {{{t+4}}} hours.