Question 1003746
This is really a multiple problem.  They will meet when the next multiple of both 7 and 4 occurs.<P>
Multiples of 7: 7, 21, 28<br>
Multiples of 4: 4, 8, 12, 16, 20, 24, 28<br>
They meet at the start after 28 minutes.  28 is the least common multiple of 4 and 7.