How do you show part c thanks

Question 6 The set V = {f : [-3, 3] - R | f(x) = a+ bx + cx2 where a, b, c, c R} is a vector space under the standard operations of pointwise addition and scalar multiplication of functions; that is, under the operations ( f + g) (x) = f(x)+ g(x), ( xf ) ( x ) = Af ( x ) , where f, g E V and X E R. (a) Identify which function z : [-3, 3] - R is the zero vector in V. Now consider the vectors f1, f2, f3 E V given below: fi (x) = 2, $2(x) = 1+ x, f3 ( x ) = x+ x2. (b) Show that the set B = {f1, f2, f3} is a linearly independent set. (c) Show that B spans V and state the dimension of V. (d) Determine whether or not the subset W of V given by W = { f : [ -3, 3] - R | f(x) = a+ ax+ x2 where a ER} is a vector subspace of V