Tea Fun Corp. manufactures tea cups. In 2020 it had $4 million worth of tea cups in inventory. In 2021 it sold $20 million worth of tea cups to consumers and had $2 million worth of tea cups in inventory. How much did the tea cups produced by Tea Fun Corp. add to GDP in 2021? a. $22 million b. $20 million C. $18 million d. $6 million