dan perhatiin pajaknya, harus di set ke dark green
If you can build the Education Network (the tv thingy (that's what you meant with comunication tower right?)), and you have built it in range of the employee's houses, you do have enough residents to advance to Engineer class. Do you have all the needs bars at green i.e. do you have enough goods (Health Food, Communicators, etc.)? And be sure to check if their taxes are set to dark green, otherwise they won't be able to advance. And you need building modules, tools and wood for each house to advance, too It's a lot to have to worry about really, but it shouldn't be too hard.
krn kk dah nanya di trit anno nya, trit gua closed, mudah2an kk yg lain bisa bantu jawab di sana, gua gak main gamenya sih so cuma andalin om gugel.