how many 4 - digit positive integers are there , where each digit is positive , and no 4 adjacent digits are same ?
"first digit . . 9 posibilities second digit , 8 possibilities third digit , 7 possibilities fourth digit , 6 possibilities . 9 * 8 * 7 * 6 = 3024 . b"
multiply(multiply(add(4, 4), add(4, 4)), multiply(add(4, 4), multiply(4, 4)))