Ah...the good old work problem.
Jim can fill the pool in 30 minutes. So, he fills 1/30 of the pool in 1 minute.
Sue can fill the pool in 45 minutes. So, she fills 1/45 of the pool in 1 minute.
Tony can fill the pool in 90 minutes. So, he fills 1/90 of the pool in 1 minute.
Now, solve for t.
If you multiply everything by t, the equation will look this way:
You can find similar "work" problems and a pretty good explanation here: "Work" Word Problems
Also, here is a related thread in this forum: http://www.mathhelpforum.com/math-he...ng-172924.html