Let $Rs.30,000$ be divided into two parts. Assume that the amount invested in the first bond as $x$, then the amount invested in the second one is $Rs(30,000-x)$.

We are given that the first bond pays $5\%$, i,e., $0.05$ in interest and the second bond $7\%$, i.e., $0.07$.

We can represent the problem using matrix multiplication as the following $1\times 2$ matrix: $\begin{bmatrix}x & 30000-x\end{bmatrix}\begin{bmatrix}0.05\\0.07\end{bmatrix}$ which is equal to the interest earned $Rs. 1800$.

Given $\begin{bmatrix}x & 30000-x\end{bmatrix}\begin{bmatrix}0.05\\0.07\end{bmatrix} = 1800$:

$\begin{bmatrix}x\times (0.05)+(30000-x)\times 0.07\end{bmatrix} = 1800$

$0.05x + 2100 - 0.07x = 1800$

$2100 - 0.02x = 1800$

$2100-1800 = 0.02x$

$0.02x = 300 \rightarrow x = \frac{1}{0.02}300$

Solving for $x$, $x = 15,000$ and $30,000-x = 15,000$.

Hence the amount has to be divided equally into two sums of $Rs.15,000$ each.