Can somebody tell me how to solve theses types of problems?

Match the one-to-one functions with their inverse functions.

Stefania pours 2 liters of orange juice and 1.5 liters of pineapple juice into a punch bowl. how many liters are in the punch bowl?

Harry owes the bank money. to repay his debt, he paid $150 back to the bank each month. after 10 months, his remaining debt was $6900. what was the original amount of harry's debt? how long did it take harry to pay back his entire debt?