Hannah buys red shirts, blue shirts, and yellow shirts at a cost of $28.75 each. which expression represents the total cost, c, of the shirts, if r represents the number of red shirts , b represents the number of blue shirts, and y represents the number of yellow shirts? plz show work and explain your work : )

a. c= 28.75 ( r + b+ y )
b. c= 28.75 ( r - b - y)
c. c= 28.75 + r + b + y
d. c= 28.75 r + b+ y