1) ((28,3+х)-17,4)+6.7=21.6
((28,3+х)-17,4)=21.7-6.7
(28,3+х)-17,4=14.9
(28,3+х)=14.9+17.4
28,3+х=32.3
х=32.3-28.3
х=4
2)101,3-(97,8-(х-4,3))=23,72
(97,8-(х-4,3))=101,3-23,72
97,8-(х-4,3)=77.58
х-4,3=97,8-77.58
х-4,3=20.22
х=20.22+4.3
х=24.52
3)91-(112,41-(х+5,5))=13,91
(112,41-(х+5,5))=91-13.91
112,41-(х+5,5)=77.09
(х+5,5)=112,41-77.09
х+5,5=35.32
х=35.32-5.5
х=29.82
4)101,2-(73,2+(х-4,3))=22,66
(73,2+(х-4,3))=101,2-22,66
73,2+(х-4,3)=78.54
х-4,3=78.54-73,2
х-4,3=5.34
х=5.34+4.3
х=9.64 :)))))