Which calculations could be used to solve this problem?

there are 21 children at corie's party. there are 2 times as many girls as boys at the party.

how many girls are at the party?

choose all answers that are correct.

a.
multiply 21 × 2. divide the product by 3.

b.
add 21 + 2. divide the sum by 3.

c.
divide 21 ÷ 3. subtract the quotient from 21.

d.
divide 21 ÷ 3. multiply the quotient by 2.