Expalin each step and write the solution in detials 

2. Let (X,A) be a measurable space, and let u A [0, 0] be a set function satisfies the following three conditions. (a) () = 0. (b) is finitely additive:* (AUB) = *(A) + *(B) for every two disjoint subsets A, B of X. (c) For every increasing sequence {A} CA, (Uk) = lim (Ak). k11 Show that is a measure.