how we find W here?

8. You invest $100 in a risky asset with an expected rate of return of 0.12 and a standard deviation of 0.15 and a T-bill with a rate of return of 0.05. What percentages of your money must be invested in the risky asset and the risk-free asset, respectively, to form a portfolio with an expected return of 0.09 ? 9%=w1(12%)+(1w1)(5%)9%=12%w1+5%5%w1 4%=7%w1w1=0.571w1=0.430.57(12%)+0.43(5%)=8.99%