Counting cell entries depending on specific condition

I need a formula that will count the total number of times a specific cell entry appears if a specific condition is met.

The spreadsheet is attached.

In sheet ‘CUSTOMER’ a formula needs to be entered into cell D2 that takes the account number displayed in A2 (1A001)and finds it in sheet ‘MISSED SCHEDULE PICKUP DATA ‘ cells B5:B827.

Each time this account number is found on a particular row the formula must look in column I on the same row and add the value from the cell onto the running total.

This will end up displaying the total number of ‘NA’ for each account number in cell D2.

Can anyone help create this formula?