how run multi threading on sequential commands

Question

hi
i have some commands that every command get the result of its previous command as argument. 
and they need about 0.03 second to run. but i need to speed up my program!

i try to perform my program with threads but because of the commands need to run one after another, i couldn't use multi-threading. because it has some error about "Object reference not set to an instance of an object".

so how can i use multi-threading in the same algorithm?
thanks in advance