At a train station, freight trains depart at a rate of 2 trains every 30 minutes and passenger trains depart at a rate of 1 train every 90 minutes. at this rate, how many total trains will depart from the station in a 12-hour period? show your work.

In my work I used t=trains and m=minutes:
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
30+30= 60m/2t
Total= 720m/24t

1:30+1:30+1:30+1:30+1:30+1:30+1:30+1:30+1:30+1:30+1:30+1:30= 4 o' clock
Total= 372m/12t

24t+12t= 36t

The answer is:
36 trains in total