Please help im struggling really bad on this one question.

How can constraints be used to model a real-world situation?

Suppose you are choosing a 6-digit personal access code. this code is made up of 4 digits chosen from 1 to 9, followed by 2 letters chosen from a to z. any of these digits or letters can be repeated. find the total number of personal access codes that can be formed. 492,804 341,172 39,917,124 4,435,236

Parallelogram efgh is a rectangle. he = 6, and fe = 8. find ge: and find fj: