`B= (2020+2021)/(2021+2022)`
`⇒B= 2020/(2021+2022) + 2021/(2021+2022)`
`mà : 2020/2021>2020/(2021+2022)`
`2021/2022>2021/(2021+2022)`
`⇒ 2020/2021 + 2021/2022 > 2020/(2021+2022) + 2021/(2021+2022)`
`⇒ 2020/2021 + 2021/2022>(2020+2021)/(2021+2022)`
`⇒ A>B`