input: from typing import List
  from math import comb
  
  def count_substrings(s: str, c: str) -> int:
      """
      You are given a string s and a character c. Return the total number of 
      substrings of s that start and end with c.
  
      Examples:
      >>> s = "abada", c = "a"
      6
      >>> s = "zzz", c = "z"
      6
  
      Constraints:
      1 <= s.length <= 10^5
      s and c consist only of lowercase English letters.
      """
  
output: 
      count = 0
      positions = [i for i, char in enumerate(s) if char == c]
      for i in range(len(positions)):
          for j in range(i, len(positions)):
              count += 1
      return count
  