2.75/(1/4+2/5x)=1/2
1/4+2/5х=2,75:1/2
1/4+2/5х=11/2
2/5х=11/2-1/4
2/5х=21/4
х=21/4:2/5
х=105/8=13,125
(2/3x+20*3/2)=43.3
2/3х+30=43,3
2/3х=43,3-30
2/3х=13,3
х=13,3:2/3
х=399/20=19,95
2.75/(1/4+2/5x)=1/2
1/4+2/5х=2,75:1/2
1/4+2/5х=11/2
2/5х=11/2-1/4
2/5х=21/4
х=21/4:2/5
х=105/8=13,125
(2/3x+20*3/2)=43.3
2/3х+30=43,3
2/3х=43,3-30
2/3х=13,3
х=13,3:2/3
х=399/20=19,95