Question 1207747
Known and understood law:  {{{SPEED*TIME=DISTANCE}}}.
Use this to fill in a data table if that helps, as I did.


Notice from the basic rule,  {{{TIME=DISTANCE/SPEED}}}.

<pre>
                   (meters per sec)   ( sec)           (meters)
                    SPEED              TIME            DISTANCE

walking with       r+1.5              200/(r+1.5)       200

not walking        r                  200/r             200

DIFFERENCE                            30


{{{highlight_green(200/r-200/(r+1.5)=30)}}}
Solve for r.</pre>
The equation then comes from the information in the table.  Matching the description.