Below are Ms. Shawn 's income's for 2016 and 2017, and estimated income from 2019. Determine if Ms. Shawn is required to make installment payments, and which alternative would be preferred for each case presented.

Case A

2019 estimated 4000

2018 1000

2017 2500

Case B

2019 estimated 3000

2018 4000

2017 3500

Case C

2019 estimated 1000

2018 3000

2017 5500

Case D

2019 estimated 4000

2018 nil

2017 3500