The following are the answers:
=oxygen equals to a charge of 2-
number of atoms is -24
=Mn equals to the charge of +3
Mn= 3+3x-24=0
let x be the charge of Cl, so:
23-3=3x
20/3=x
=6.67 or 7
x= 7
= Cl has a charge of +7
You are right about your answers