Hello, I need help with the following problem in Finance.

A portfolio gives a 10% return with a standard deviation of 18%. You would like the standard deviation to drop to 14%. What should you do?

What should you do if you want the standard deviation to rise to 23%?

Our notes provide us with the correct answers, but I don't understand how they were reached. Please provide a step by step calculations on how these

answers were reached.

Here are the answers in our notes:

For the standard deviation to drop to 14% it says the answer is to add more risk-free assets until they account for 4/18 of the portfolio. Don't understand how 4/18 was reached or why that is the solution?

For the standard deviation to rise to 23%, it says the answer is to use debt to finance an increase in the size of the portfolio by 5/18. Again, how was 5/18 calculated and why?