Save And Dispence-Is it supposed to Autocalculate the amount?

Why is it asking me to enter the amount if I have chosen 22 tablets which are configured in the pharmacy inventory?
or are we supposed to manually calculate the price of 22 tablets and then enter it for it to reflect on billing?

i havent entered the NDC no which is not available to me for drugs.

is it the NDC no like in he picture that auto calculates the amount?