Hello there!  Can you please provide me with a list of all of the different payment method code types?
select distinct payment_method_code from invoices
Awesome!  Of these different codes, can you tell me which individual code was used by the largest number of orders?
select payment_method_code from invoices group by payment_method_code order by count ( * ) desc limit 1
Great!  Can you please tell me what is the total number of orders that used MasterCard?
select count ( * ) from invoices where payment_method_code = "MasterCard"