\[5x-3a-2x-5a=4a,\quad 3x=12a,\quad x=4a.\]
\[x+a+x+2a-x+3a=8a,\quad x+6a=8a,\quad x=2a.\]
\[\left(\frac34+\frac23-\frac7{12}\right)x-\frac25+0.6+0.3=5.8.\] \[\frac56x+0.5=5.8,\quad \frac56x=5.3,\quad x=5.3\cdot\frac65=6.36.\]
\[3x+2a=2a-b-2a+5b=4b-2a,\quad 3x=4b-4a,\quad x=\frac43(b-a).\]
Ответ: 1) \(x=4a\); 2) \(x=2a\); 3) \(x=6.36\); 4) \(x=\frac43(b-a)\).