Remember that
Compatible numbers are pairs of numbers that are easy to add, subtract, multiply, or divide mentally
so
we have
5,391 divided by 77
Find out the compatible numbers
5,391 -------> 5,400
if the denominator is 5,400
then
find the prime factors
prime factors=2,3,5
75=5^3 -----> is compatible
All Factors of 5400: 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 25, 27, 30, 36, 40, 45, 50, 54, 60, 72, 75, 90, 100, 108, 120, 135, 150, 180, 200, 216, 225, 270, 300, 360, 450, 540, 600, 675, 900, 1080, 1350, 1800, 2700 and 5400
you need to find a factor compatible with the number 77
the number is 75
therefore
5,400 /75=72