The area of a rhombus is 30 $cm^2$. One of the diagonals is 6 cm. We need to find the length of the other diagonal.

1. Problem Description

The area of a rhombus is 30 $cm^2$. One of the diagonals is 6 cm. We need to find the length of the other diagonal.

2. Solution Steps

The area of a rhombus is given by the formula:

$Area = \frac{1}{2} * d_1 * d_2$, where $d_1$ and $d_2$ are the lengths of the diagonals.

We are given that the area is 30 $cm^2$ and one diagonal is 6 cm. Let $d_1 = 6$ cm.

Then, we have

$30 = \frac{1}{2} * 6 * d_2$

$30 = 3 * d_2$

$d_2 = \frac{30}{3}$

$d_2 = 10$ cm

3. Final Answer

The length of the other diagonal is 10 cm.

So the answer is C. 10 cm.