What is the world beta in the U.S. when the S&P 500 & the Vanguard World Stock ETF have a covariance of returns of 0.45, the S&P 500 has a variance of returns of 0.23, & the Vanguard World Stock ETF has a variance of returns of 0.37? a. 1.96 b. 1.22 c. 0.62 d. 1.61