How do I write a expository writing on the prompt "If the trends casued by technology grow, how will they affect society in thirty or sixty years time" on future worlds
Expository writing is writing meant to explain something, so you should focus on explaining what trends technology has caused. The growth of micro-circuitry has led to greater processing power in smaller devices. e.g. an ipad has the same processing power that desktops had 10 years ago; an iPhone has as much processing power as Star Trek tricorders are portrayed as having. Increasing reliance on renewable or Green energy may make longer distance travel possible.
You should stay away from stating whether these trends are good or pad (persuasive writing). Since the prompt mentions future worlds, you should assume that we will soon start terraforming Mars, and any other potentially inhabitable body in the Solar System (e.g. Titan, Europa, Ganymede).