Forumla (pulling data)

I have two objects

1) Orders

2) Quality Check

Orders has a field called quantity received (numeric) and a unique identifier as gate entry (number data field).

In my Quality Check object.

I created a connection with the orders object.

I want to insert an formula field that allows be to pull the quantity received data into the quality check object.

---- my thinking.

So the product is received at the gate and a gate entry form is filled with various details.

Now at the time of quality checking, QA picks the data via selecting the gate entry number.

Which then should populate a few fields in the form view to allow him to see who the supplier is and what quantity was received.

Then he enters the accepted quantity

and then a formula auto calculates the rejected quantity (Which I have been able to do).

But how do pull data based on gate entry selection in the form view of Quality Check Object.

please advice or lead me to the correct resource. I would really appreciate it.