Provide your best answer for the following math problem. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The problem is: if rs . 420 amount to rs . 540 in 4 years , what will it amount to in 6 years at the same rate % per annum ?
s . 600
Rs. 936.