To find the value of \( K \) in the investment ratio of A, B, and C, we start by representing their investments mathematically based on the given ratio.

Given that the investments are in the ratio of \( 3 : 2 : K \), let's denote the actual amounts invested by A, B, and C as \( 3x \), \( 2x \), and \( Kx \) respectively, where \( x \) is a common multiplier.

From the problem, we know:

1. C's share is Rs 120 more than A's share: 
   \(Kx = 3x + 120\)
2. B's share is Rs 30 less than A's share: 
   \(2x = 3x - 30\)

We tackle each equation separately:

1. From the second equation: 
   \(2x = 3x - 30 \Rightarrow 3x - 2x = 30 \Rightarrow x = 30\)
2. Substituting \(x = 30\) into the first equation: 
   \(Kx = 3x + 120\)
   Substituting \(x = 30\):
   \(K \times 30 = 3 \times 30 + 120\)
   \(30K = 90 + 120\)
   \(30K = 210\)

Solving for \( K \):

1. \(K = \frac{210}{30} = 7\)

Thus, the value of \( K \) is 7.