2) 21*5/(25*7)-(3/16)х=11/20
(3/5)-(11/20)=(3/16)х
1/20=3х/16
х=(1/20):(3/16)
х=16/(20*3)
х=4/15
3) (х-1 1/3):1 5/12=4/51
(х-1 1/3)=(1 5/12)*(4/51)
(х-1 1/3)=(17/12)*(4/51)
(х-1 1/3)=1/9
х=1 3/9 +1/9
х=1 4/9
