input: Write a python function to find the sum of an array of numbers using a class.
  assert SumArray([1, 2, 3, 4]).get_sum() == 10
  assert SumArray([10, 20, 30, 40]).get_sum() == 100
  assert SumArray([5, 15, 25, 35]).get_sum() == 80
output: class SumArray:
      def __init__(self, numbers):
          self.numbers = numbers
  
      def get_sum(self):
          return sum(self.numbers)