`a, ( - 8 ) . ( - 8 ) . ( - 8 ) . ( - 8 ) . ( - 8 ) . ( - 8 )`
`= ( - 8 )^6`
`= 8^6`
`b,( - 7 )^4 . ( - 27 ) . ( - 3 )`
`= ( - 7 )^4 . ( - 3 )^3 . ( - 3 )`
`= ( - 7 )^4 . [ ( - 3 )^3 . ( - 3 ) ]`
`= ( - 7 )^4 . ( - 3 )^4`
`= [ ( - 7 ) . ( - 3 )]^4`
`= 21^4`