Factorise each of the following expressions: (a) #x^2 + 6x + 8# (b) #x^2 - 5x + 6 #(c) #x^2 + 4x -21#(d) #x^2 + x - 2 #(e) #x^2 + 2x – 35#(f) #x^2 - 10x + 24#