ABCD is a parallelogram such that AF =7 cm, FB =3 cm and EF =4 cm, length FD = equals

ABCD is a parallelogram such that $\displaystyle \mathrm{AF}=7 \mathrm{~cm}, \mathrm{FB}=3 \mathrm{~cm}$ and $\displaystyle \mathrm{EF}=4 \mathrm{~cm}$, length FD = equals