`2A = 2(3 + 3^2 + 3^3 + ... + 3^{2020})`.

`2A = 23 + 23^2 + 23^3 + ... + 23^{2020}`

`2A = 23^1 + 23^2 + 23^3 + ... + 23^{2020}`

`2A + 3 = (23 + 23^2 + 23^3 + ... + 23^{2020}) + 3`

`2A + 3 = 3 + 23 + 23^2 + 23^3 + ... + 23^{2020}`

`2A + 3 = 3^1 + 23^1 + 23^2 + 23^3 + ... + 23^{2020}`

`2A + 3 = 33^0 + 23^1 + 23^2 + 23^3 + ... + 23^{2020}`

`2A + 3 = 3^1 + 23^1 + 23^2 + 23^3 + ... + 23^{2020}`

`2A + 3 = 3 + 23 + 23^2 + 23^3 + ... + 2*3^{2020}`

`3A = 3(3 + 3^2 + 3^3 + ... + 3^{2020})`

`3A = 3^2 + 3^3 + 3^4 + ... + 3^{2021}`

`3A - A = (3^2 + 3^3 + 3^4 + ... + 3^{2021}) - (3 + 3^2 + 3^3 + ... + 3^{2020})`

`2A = 3^{2021} - 3`

`2A + 3 = 3^{2021}`

`2A + 3 = (3^{2021} - 3) + 3`

Giải phưởng trình, ta có  `:`

`2A + 3 = 3^{x-1}` , vậy `3^{2021} = 3^{x-1}`

Do đó `x - 1 = 2021`

`x = 2021 + 1 = 2022`