So let me get this straight. i will use an example.
The us has a Hybrid unit that lost 2-steps in battle. So for the first step lost to be replace it will cost the US player "1.5 replacement points" since that is the highest armor replacement value for the US and plus the US player has to replace armor first. The 2nd step lost to be replace will cost "1 replacement points" since that is the cost for infantry.
So in total it will cost the US player 2.5 points to replace 2 step losses on a Hybrid Unit.
If it's an M4 Firefly it is 1.5 armor ( are those only British?). If it's a M4 Sherman it's only 1 armor.
The infantry is mechanized infantry. So it's either .5 inf and .5 arm or 2 Inf. (according to the latest chart)