Explain the gains from trade that arise for both buyers and sellers in the following transactions:

a. Neighbors Jordan and Chelsea are both working parents. They are able to hire a single babysitter to care for both of their toddlers for 75% of what they would collectively have to pay two separate babysitters. 

b. Elijah decides that his family should eat more healthy meals, but they are short on time. He buys a subscription that sends healthy preplanned meals to his home three times a week. 

c. Callie accepts an extra shift at work and hires a cleaning service to clean her apartment.