Thea has a key on her calculator marked X. If an integer is displayed, pressing theX key chops off the first digit and moves it to the end. For example, if $6138$ is on the screen, then pressing the X key changes the display to $1386$. Thea enters a positive integer into her calculator, then squares it, then presses the X key, then squares the result, then presses the key again. After all these steps, the calculator displays $243$. What number did Thea originally enter?

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?