`a, - 3 1/2 - 2 1/4`
`= ( - 7 )/2 - 9/4`
`= ( - 14 )/4 - 9/4`
`= ( - 23 )/4`
`b, 1/12 - ( - 1/6 - 1/4 )`
`= 1/12 - ( - 2/12 - 3/12 )`
`= 1/12 - ( - 5 )/12`
`= 1/2`
`c, 2/5 + ( - 4 )/3 + ( - 1 )/2`
`= 24/60 + ( - 80 )/60 + ( - 30 )/60`
`= ( - 56 )/60 + ( - 30 )/60`
`= ( - 43 )/30`
`d, 1/3 - [ ( - 5 )/4 - ( 1/4 + 3/8 )]`
`= 1/3 - [ ( - 5 )/4 - ( 2/8 + 3/8 )]`
`= 1/3 - [ ( - 5 )/4 - 5/8 ]`
`= 1/3 - [ ( - 10 )/8 - 5/8 ]`
`= 1/3 - ( - 15 )/8`
`= 8/24 - ( - 45 )/24`
`= 53/24`