Assume a perfect capital market in which investors are constrained to holding portfolios that consist only of a single risky asset, that borrowing or lending at a riskless interest rate is possible, and that in equilibrium the following holds:

Security i: ri $=26\%$ sigmai $=15\%$

Security j: rj $=18\%$ sigmaj $=9\%$

What is the riskless rate of interest in this market $?$