Suppose that Treasury bills offer a return of about 6% and the expected market risk premium is 8.5%. The standard deviation of Treasury-bill returns is zero and the standard deviation of market returns is 20%. Use the formula for portfolio risk to calculate the standard deviation of portfolios with different proportions in Treasury bills and the market. (Note: The covariance of two rates of return must be zero when the standard deviation of one return is zero.) Graph the expected returns and standard deviations.

https://www.chegg.com/homework-help/suppose-treasury-bills-offer-return-6-expected-market-risk-p-chapter-7-problem-22p-solution-9780077356385-exc?hwh_cr=1

Can someone explain from step 3 onwards, as the explanation is too brief.

For step 4, why do we have to add the numbers together (0.06+0.85) . Where is 0.145 coming from?

And isn't this 0.085?

Thanks!