Varying amounts of pectin were added to canned jellies, to study the relationship between pectin concentration in % (x) and a firmness index (y). The means and standard deviations of the x and y values were  = 3, sx = 0.5,  = 50, sy = 10. The correlation between curing time and firmness was computed to be r = 0.5. Find the equation of the least-squares line to predict firmness from pectin concentration.