Question 1050863
In order to solve this problem, the following formula is needed:

Speed = {{{distance/time}}}

Tim can run three miles in 20 minutes. Plug in what you know:

Speed = {{{3 miles/ 20 minutes}}}
Speed= 0.15 mi/ minutes

If he maintains his speed, how long will it take him to run nine miles?

Again, plug in what you know:

Speed= {{{distance/time}}}
0.15 mi/ minutes = {{{9 miles / time}}}

multiply each side by time:
(0.15 mi/ minutes)(time) = 9 miles

divide each side by 0.15 mi/ minutes:
time= {{{9 / 0.15 }}}
time= 60 minutes

It will take Tim one hour, or 60 minutes, to run nine miles.
Another way to solve this problem is by realizing that if Tim can run 3 miles in twenty minutes and by multiplying 3 by 3, you get 9. When you multiply 3 by 20 minutes, you also get 60 minutes.