oh and here's some tips at level 6 make sure that atleast 3 cannons are upgraded and just buy as many cannons as possible don't upgrade any more than 5 but have atleast 3 and at level 11 sell all of them before level 11 and buy as manny electric towers as possible!
 "Zening"){kind=icon}
 "Shock Defence"){kind=icon}
 "UPGRADE COMPLETE!"){kind=icon}