texd hits the nail on the head - forget mileage, use points.

You have 16 trips. Flying from MOB requires that you fly through IAH on CO. One of your trips is to IAH so that leaves 15 trips where you get 4 points for the RT + the two for the IAH or 62 for the year. 28 more points get you the 90 for Plat so - 7 of your trips, scheduled at the relative last minute due to business complications flown at H or Y will add 28 segments and give you Plat.

Have fun!