Question 5376
Set this up by determining how much distance each covers in one minute:

John runs {{{1/9}}} of the distance each minute
Henry runs {{{1/6}}} of the distance each minute

When running from opposite ends they are covering a distance of John + Henry, or
{{{1/9+1/6}}} = {{{2/18+3/18}}}={{{5/18}}}

After the first minute they are {{{5/18}}} of the distance
After the second minute they are {{{10/18}}} of the distance... and so on

Set this up as a proportionality {{{(Rate)/(total distance) = (1 minute)/(total time)}}}:
{{{(5/18)=1/x}}}

Cross multiply:
{{{5x=18}}}
Divide both sides by 5
{{{x=18/5 = 3.6}}}
So it took them 3.6 minutes to meet.