240 :( x+3)-5=7
240:(х+3)=7+5
х+3=240:12
х+3=20
х=20-3 =17
240:(x+3)-5=7
240:(x+3)=5+7
240:(x+3)=12
x+3=240:12
x+3=20 x=20-3
x=17
Проверка:
240:(17+3)-5=7
12-5=7
7=7