So essentially, every hour they move (40+10=50 miles per hour). So we know that every hour their distance diminishes by 50 miles - so how many hours are needed for the distance to get from 750 to 0?
We calculate like this:
750/50=15
this means that they need 15 hours!
so, what is 15 hours after 11 am?
after 1 hrs it's noon
12 hours later (total of 13 hours) it will be midnight
and two hours after midnight the 15 hours will have passed, so the answer is: they will meet at 2 AM of the following day!