The digit positive integer is the sum of all of its digits. For example, the digit sum of the integer 1234 is 10, since 1 + 2+ 3 + 4 = 10. Find all three-digit positive integers whose digit sum is exactly 9.

This is the answer that I got, it can also be found out through running the code by pressing the green button:

108

117

126

135

144

153

162

Well, but there is another problem that I do not know how to solve. The problem can be found here: https://www.cemc.uwaterloo.ca/resources/potw/2019-20/English/POTWE-19-AE-02-P.pdf. If you find out the answer, please leave a comment!