3/7 + 4/21 - 1/3 = denga cara

3/7 + 4/21 =
3/7 x 3/3= 9/21
9/21 + 4/21= 13/21
13/21-1/3=
1/3 x 7/7 = 7/21
13/21- 7/21= 6/21

3/7 + 4/21 - 1/3 =
(3×3)/(7×3) + 4/21 - (1×7)/(3×7) =
9/21 + 4/21 - 7/21 =
13/21 - 7/21 =
6/21