`a, ( 187 - 23 ) - ( 20 + 187 )`
`= 187 - 23 - 20 - 187`
`= ( 187 - 187 ) - ( 23 + 20 )`
`= 0 - 43`
`= - 43`
`b, 2^3 . 3 + 2^3 . 7 - 5^2`
`= 8 . 3 + 8 . 7 - 25`
`= 8 . ( 3 + 7 ) - 25`
`= 8 . 10 - 25`
`= 80 - 25`
`= 55`
`c, ( - 50 - 79 + 143 ) - ( - 79 + 25 - 143 )`
`= - 50 - 79 + 143 + 79 - 25 + 143`
`= ( - 50 - 25 ) - ( 79 - 79 ) + ( 143 + 143 )`
`= - 75 - 0 + 286`
`= - 75 + 286`
`= 211`