Question 55119
The slope, m, is defined as {{{m=(y[2]-y[1])/(x[2]-x[1])}}}.  It doesn't matter which ordered pair is {{{x[1]}}},{{{y[1]}}} and {{{x[2]}}},{{{y[2]}}} because you'll get the same answer.  Using substitution we get {{{2=(r-3)/(5-2)}}}, which simplifies to {{{2=(r-3)/3}}}.  Multiplying both sides by 3 gives us {{{6=r-3}}} and adding 3 to both sides gives us {{{r=9}}}.