tolong bantuannya kaka

berikut jawabannya ya...
a. 2K+Mn+4O=0
2.(+1) + Mn + 4.(-2) = 0
(+2) + Mn + (-8) =0
Mn = +6
b. N + 4H = +1
N + 4.1 = 1
N + 4 = 1
N = -3
c. Na + H = 0
1 + H = 0
H = -1
d. 2.K + 2.Cr + 7.(O) = 0
2.1 + 2.Cr + 7.(-2) = 0
2 + 2.Cr + -14 = 0
2.Cr = +14 - 2 = +12