Let's say the total work is to eat 24 ladoos. (Hint : take lcm of days i.e. 6,8 and 3 to make the calculation easier).
Given that A can complete the work alone in 6 days. So, A eats 4 ladoos per day.
Similarly, B eats 3 ladoos per day. So, A + B eat 7 ladoos per day.
Let's assume C eats c ladoos per day. Therefore, A + B + C eat 7 + c ladoos per day.
And they take 3 days to finish 24 ladoos.
Therefore, (3)(7+c) = 24. This gives c = 1.
So, out of 24 ladoos :
A eats total 4*3 = 12 ladoos
B eats total 3*3 = 9 ladoos
C eats total 1*3 = 3 ladoos
And the ratio comes out as 4 : 3 : 1 (A : B : C)
So, the amount C receives will be [1/(4+3+1)]*3200
which comes out to be (1/8)*3200 = 400