SASMO 2020 Grade 7 Question 1

Exam grading: platform starts at 0; Q1–15 award 2 points each, Q16–25 award 4 each; no penalties; maximum 70. Official reference: starts at 15; Section A +2/−1/0 for correct/incorrect/blank, Section B +4/0/0; maximum 85. Duration: 90 minutes (official-reference default).

Find $2020\times2020-2019\times2021$.