Answer : The mass of
required are, 35 kg
Explanation :
First we have to calculate the mass of
.
The first step balanced chemical reaction is:

Molar mass of
= 115 g/mole
Molar mass of
= 87 g/mole
Let the mass of
be, 'x' grams.
From the balanced reaction, we conclude that
As,
of
react to give
of 
So,
of
react to give
of 
And as we are given that the yield produced from the first step is, 65 % that means,

The mass of
obtained = 0.4542x g
Now we have to calculate the mass of
.
The second step balanced chemical reaction is:

Molar mass of
= 87 g/mole
Molar mass of
= 55 g/mole
From the balanced reaction, we conclude that
As,
of
react to give
of 
So,
of
react to give
of 
And as we are given that the yield produced from the second step is, 80 % that means,

The mass of
obtained = 0.2296x g
The given mass of Mn = 8.0 kg = 8000 g (1 kg = 1000 g)
So, 0.2296x = 8000
x = 34843.20 g = 34.84 kg = 35 kg
Therefore, the mass of
required are, 35 kg