Find each missing side, then the perimeter

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

Ineed the solution to this problem and the steps.

X=-3y-5 3x+9y=7 how can u solve this?