-17/21+9/14=? 3,9+(-3,9)=? 2,77+(-1/4)=?

Question

-17/21+9/14=?
3,9+(-3,9)=?
2,77+(-1/4)=?

Answer 1

-17/21 + 9/14 = -34/42 + 27/42 = (-34+27)/42 = -7/42 = -1/6
3,9 + (-3,9) = 3,9 - 3,9 = 0
2,77 + (-1/4) = 2,77 - 1/4 = 2,77 - 0,25 = 2,52