Hej!
a]
[tex]5x+8=2x-4\\\\5x-2x=-4-8\\\\3x=-12 \ \ |:3\\\\\huge\boxed{x=-4}[/tex]
b]
[tex]7a-14=3a+8\\\\7a-3a=8+14\\\\4a=22 \ \ |:4\\\\\huge\boxed{a=5,5}[/tex]
c]
[tex]-9y-5=-10y+4\\\\-9y+10y=4+5\\\\\huge\boxed{y=9}[/tex]