(3,9+х)-1цел3/4=5,25
(3,9+х)-1,75=5,25
3,9+х=5,25+1,75
3,9+х=7
х=7-3,9
х=3,1
3,9+x-1.75=5.25
x=5.25-3.9+1.75
x=3.1
(3,9+х)-1цел3/4=5,25
(3,9+х)-1,75=5,25
3,9+х=5,25+1,75
3,9+х=7
х=7-3,9
х=3,1
3,9+x-1.75=5.25
x=5.25-3.9+1.75
x=3.1