Kevin sold a box of 28 books at a yard sale for a total of $54.64. he sold the paperback books for $1.68 each and sold the hardcover books for $2.44 each. which system of equations can be used to determine the number of $1.68 paperback books, x, and the number of $2.44 hardcover books, y, that were sold at the yard sale?

a.
x + y = 28
1.68x + 2.44y = 54.64

b.
2.44x - 1.68y = 28
x + y = 54.64

c.
x + y = 28
2.44y = -1.68x + 54.64

d.
y = x - 54.64
1.68x + 2.44y = 28