Form the smallest and greatest 6-digit numerals by repeating any 2 digits from 7,9,5,4.

Form the largest and smallest 4-digit numbers using each of digits 7, 1, 0, 5 only once.

Find the difference between the greatest and the smallest four-digit numbers formed by using all the digits 8, 6, 7 and 4.

Find the difference between the greatest 5-digit number and the greatest 4-digit number formed using the digits 7, 6, 2, 5, 1 when the repetition is not allowed.