The U.S. online grocery market is estimating sales worth approximately $29.7 billion by 2021. One factor that influences the U.S. online sales is the median U.S. income. Assume online sales is in billions of dollars and U.S. income is in thousands of dollars. Using the Ordinary Least Squares method, the regression equation was estimated as: =-61 + 2.1 x1 Find the predicted US online sales amount if U.S. median income is $45,000, and interpret the slope of the explanatory variable. a) $94.4 billion. For every $1,000 increase in U.S. median income, U.S. online sales increases by $2.1 billion. b) $33.5 billion. For every $1,000 increase in U.S. median income, U.S. online sales increases by $2.1 billion.