Which explanation best describes how to solve this problem?

marcia covered her kitchen floor with twice as much tile as her bathroom floor. she tiled 15 square feet of her bathroom floor. she also tiled a 9-square-foot area by her front door.

how many square feet of her house did marcia tile altogether?

a.
divide 15 by 2. then add 9 and 15 to the quotient.

b.
add 15 and 9 and multiply the sum by 2.

c.
multiply 15 × 2. then add 15 and 9 to the product.

d.
subtract 9 from 15. then multiply the difference by 2.