Assign oxidation number for all the elements in each of the compound

Question

KMnO4
(NH4)2HPO4
P4O6

Answer 1

KMnO4:

K: +1
Mn: +7
O: -2

(NH4)2HPO4:

N: -3 (because each ammonium group has a total charge of +1 and there are 2 of them)
H: +1
P: +5
O: -2

P4O6:

P: +3
O: -2