Can we predict the calories in a fast-food product if we know the amount of protein in that product? Several fast-food products were examined and the number of calories and amount of protein (in grams) were recorded. In the sample, the smallest and largest amounts of protein were 4 grams and 22 grams, respectively. Analyzing the data resulted in the following information:

Correlation of Protein and Calories = r = -0.87

The regression equation is Calories = 302.5 - 0.51(Protein)

What is the value of the slope of the least squares regression line?