`\text{a)} 1/3 - 1 3/4 + 1/12`
`= 1/3 - 7/4 + 1/12`
`= 4/12 - 21/12 + 1/12`
`= - 16/12 = - 4/3`
`\text{b)} (2020/2021)^0 - (- 1/2)^2 - |- 3 + 1/4|`
`= 1 - 1/4 - |- 12/4 + 1/4|`
`= 4/4 - 1/4 - 11/4`
`= -8/4 = - 2`
`\text{c)} x - 4/5 = 3/4`
`x = 3/4 + 4/5`
`x = 31/20`
`\text{d)} 1/2 + 2/9x = (-2/3)^2`
`1/2 + 2/9x = 4/9`
`2/9x = - 1/18`
`x = - 1/18 : 2/9`
`x = - 1/4`