(х+3):2+(х+3)+х=42м
(х+3):2+х+х+3=42м
(х+3):2+2х+3=42м
(х+3):2+3+2х=42м
(х+3):2=42-3-2х
(х+3):2=39-2х
х=((39-2х)*2)-3
х=78-4х-3
х=75-4х
х+4х=75
х=75:5
х=15
(15+3):2+(15+3)+15=42м
ответ:х=15
(х+3):2+(х+3)+х=42м
(х+3):2+х+х+3=42м
(х+3):2+2х+3=42м
(х+3):2+3+2х=42м
(х+3):2=42-3-2х
(х+3):2=39-2х
х=((39-2х)*2)-3
х=78-4х-3
х=75-4х
х+4х=75
х=75:5
х=15
(15+3):2+(15+3)+15=42м
ответ:х=15