Question 126231
First think about what is generally true. They meet 
somewhere in the middle, so the sum of their walks
is 4 miles. They leave at the same time, so the
time each spends walking is exactly the same.
Now you can start
Let {{{d[f]}}} = distance in miles Fred walks
Let {{{d[j]}}} = distance in miles Jon walks
{{{d[f] + d[j] = 4}}} what I just said
Let {{{t}}} = time in hours they both spend walking
{{{d[f] = 3t}}}
{{{d[j] = 2t}}}
Now add these equations
{{{d[f] + d[j] = 3t + 2t}}}
{{{4 = 3t + 2t}}}
{{{5t = 4}}}
{{{t = 4/5}}} hr
or
They will meet in {{{(4/5)60 = 48}}} minutes answer