3) 12 marks] Determine whether 2r is O(g(x)) for each of these functions g(x) a) g(r)-x b) g(r)-x2 c) g(x)=2x d) g(r)-3 4) [12 marks] Use summation notation to determine how many times line 4 is executed in the algorithms below (this corresponds to the value of sum). What is the Big O of each? a) ine 1: sum:0 Line 2: for i 1 to n Line 3: for j := 1 to n Line 4 //