`a, ( 36 - 4 xx 9 ) : ( 1/2 + 1/3 + 1/4 + 1/5 )`
`= ( 36 - 36 ) : ( 1/2 + 1/3 + 1/4 + 1/5 )`
`= 0 : ( 1/2 + 1/3 + 1/4 + 1/5 )`
`= 0`
`b, 3/4 xx 7/8 + 3/4 xx 5/8 - 3/4 : 8/4`
`= 3/4 xx 7/8 + 3/4 xx 5/8 - 3/4 xx 4/8`
`= 3/4 xx ( 7/8 + 5/8 - 4/8 )`
`= 3/4 xx 1`
`= 3/4`