Answer: Triple the amount invested in the risky portfolio
Step-by-step explanation:
The Risk-free rate by definition has no risk (or very little risk) so if the amount invested in this asset is tripled, the risk will not triple.
Decreasing the amount invested in the risky portfolio will decrease the risk of the complete portfolio because you have divested from asset giving your portfolio risk.
Doing nothing will neither increase nor decrease your portfolio's risk.
Best option therefore is to triple the amount invested in the risky portfolio because by investing three times more in a risky portfolio, you are now 3 times at risk.