3 × 3 + 3 : 3 + 3 × ( a : 3 - 3 ) = 2020
● 9 + 1 + 3 × ( a : 3 - 3 )= 2020
● 10 + 3 × ( a : 3 - 3 ) = 2020
● 3 × ( a : 3 - 3 ) = 2020 - 10
● 3 × ( a : 3 - 3 ) = 2010
● a : 3 - 3 = 2010 : 3
● a : 3 - 3 = 670
● a : 3 = 670 + 3
● a : 3 = 673
● a = 673 × 3
● a = 2019