I have some math problems that I'm confused on...

I was given these formulas to work with:

If 500 fleas1) How many fleas will there be in 3 days?triplein their population every 18 hours:

I got 40500, but will someone confirm whether this is right?

2) How long will it take for there to be 1200 fleas?

I got 14.34 hours,but again, I'm not too confident in my solution. Could someone possibly confirm this as well?