Acompany receives a discount of 10% per unit for all units ordered over a quantity of 50. suppose cell b1 of an excel sheet contains the quantity of units ordered and that cell b2 contains the unit price. the excel formula that best expresses the calculation of the cost of the order is a. =if(b1< =50, 50*b2+(b1-50)*(0.9*b2), b1*b2) b. =if(b1< 50, 50*b2+(b1-50)*(0.9*b2), b1*b2) c. =if(b1> =50, 50*b2+(b1-50)*(0.9*b2), b1*b2) d. =if(b1> 50, 50*b2+(b1-50)*(0.9*b2), b1*b2)