д) 1/7 + 2/21 + 3/7 = $3/21$ + $2/21$ + $9/21$ = 14/21 = 2/3

в) 7/10 + 2/15 + 11/30 = $21/30$ + $4/30$ + $11/30$ = 36/30 = 6/5

е) 1/15 + 2/45 + 7/15 = $3/45$ + $2/45$ + $21/45$ = 26/45

ж) 1/12 + 1/8 + 1/12 = $2/24$ + $3/24$ + $2/24$ = 7/24