Well I don't see them excercising the 90 bus option, that would make no sense as you would have an excess of CNG buses that you can't put anywhere else as Gleason, WF, SC & CP are the only CNG contenders
Now looking at it they could exercise the 30 bus option
As looking at it there would be 22 Orion V CNGS left to displace after the 74 order is done.
30-22 = 8
Still have 8 new buses but wait
You still have 25 remaining old C40s left
So you could knock off 8 of those to reserve leaving 17 old c40lfs active