`d, (-1/2)^2 : 1/4 + 2 . (-1/3)^3`
`= 1/4 : 1/4 + 2 . 1/27`
`= 1 + 2/27`
`= 27/27 + 2/27`
`= 29/27`
`a, (14/23 - 5/21) - (4/23 - 3/4) - 16/21`
`= 14/23 - 5/21 - 4/23 + 3/4 - 16/21`
`= ( 14/23 - 4/23 ) - ( 5/21 + 16/21 ) + 3/4`
`= 10/23 - 1 + 3/4`
`= 40/92 - 92/92 + 69/82`
`= 17/92`
`c, 1/7 . (-3/8) + 1/7 . (-13/8)`
`= 1/7 . ( (-3)/8 + (-13)/8 )`
`= 1/7 . (-16)/8`
`= 1/7 . (-2)`
`= (-2)/7`