2/9-7/16 * 2/9=2/9*(1-7/16)=2/9 *9/16=1/8
4/5 * 7/9 * 5/8=4/5 *5/8 *7/9=1/2 *7/9=7/18
5/7 *16 *21/5=5/7 *21/5 *16 =3*16=48