3) a) 2 {-8-5-[-7-2-(16-11-7)]} b) 2.{-8-3-1-7-2-(18-12-9)]} c) 4.{-2-[7-3-(-4-8+ 16)]:(-5)} d) 2.{3-4-[-8-2-(- 12 +4+3)]}​