Write methods called sum and average that return the sum of all values in the list and the average value as a real number, respectively. For example, if a variable called list stores [11, –7, 3, 42, 0, 14], the call of list.sum() should return 63 and the call of list.average() should return 10.5. If the list is empty, sum should return 0 and average should return 0.0.