Question 1003841
That set of questions is for three different resulting values for what is the same variable.  


Basic travel rates rule is RT=D to relate rate, time, and distance.


Setup a data table, fill in what is given, use variables if possible for what is not known, look for equations to form; solve the equations, equation, or system of equations as fits the question or objectives.



<pre>
             rate           time           distance

GOING         30            {{{90/30=3}}}         90

RETURN        r             {{{90/r}}}            90

Total                       {{{90/r+3}}}            180
</pre>

The speed for the whole trip is  {{{180/(90/r+3)}}}.




Let P be the average rate for the whole round trip.
{{{highlight(P=180/(90/r+3))}}}.
Expect P to be any given constant, positive value greater than 30; solve the formula for r.