input: def find_primes_up_to(limit: int) -> List[int]:
      """ Find all prime numbers up to a given limit.
      >>> find_primes_up_to(10)
      [2, 3, 5, 7]
      >>> find_primes_up_to(20)
      [2, 3, 5, 7, 11, 13, 17, 19]
      """
output:     primes = []
      for num in range(2, limit + 1):
          is_prime = True
          for i in range(2, int(num**0.5) + 1):
              if num % i == 0:
                  is_prime = False
                  break
          if is_prime:
              primes.append(num)
      return primes