The tens digit of a certain number is five more than the units digit. The sum of the digits is 9. Find the number.

the tens digit = n
the units digit = n-5

n + n-5 = 9
2n = 9+5
2n = 14
n = 7  ←  the tens digit

the units digit = n-5 = 7 - 5 = 2

the number is 72