This question involves the idea of the sum of n terms of an arithmetic series. According to the question, Ramjanam pays the total loan in installments where each installment can be represented as a, a + 400, a + 800, a + 1200, …, up to 30 terms.

Given:
- Total loan amount \( \rm S_{30} = 189000 \)
- Increase in installment amount every month \( \rm d = 400 \)

Let's denote:
- The first installment amount as \( \rm a_1 \)
- Total number of months as \( \rm n = 30 \)

We can use the formula for the sum of the first \( \rm n \) terms of an arithmetic series:

\( \rm S_n = \frac{n}{2}(2a_1 + (n - 1)d) \)

Substitute the given values:

\( \rm 189000 = \frac{30}{2}(2a_1 + (30 - 1) \times 400) \)

\( \rm 189000 = 15(2a_1 + 29 \times 400) \)

\( \rm 12600 = 2a_1 + 11600 \)

\( \rm 2a_1 = 12600 - 11600 \)

\( \rm 2a_1 = 1000 \)

\( \rm a_1 = \frac{1000}{2} \)

\( \rm a_1 = 500 \)

So, the amount of the first installment is Rs 500.