Adam calculates his annual commission, y, using the model y = 0.28x, where x represents his total sales for the year. what is the meaning of the x-intercept in the model? a) the x-intercept represents adam's base pay b) the x-intercept represents the highest salary adam can earn c) the x-intercept represents adam's total sales when he earned no commission d) the x-intercept represents adam's commission pay when he had zero total sales