What does “our prime purpose in life is to help people and if you do not help them don't hurt them”mean

It simply means to everyone you have the opportunity to help,offer the appropriate assistance and in no way should you instead of offering assistance, cause them pain.

the correct answer is “opportunity cost”. opportunity cost is what a company misses out because it decided in one option over another one. in this case, the company decided to invest in building a factory so it gave up another possible benefit or profit in order to achieve success with the factory.  

trade-off is not the correct answer since it is a situation in which you accept losing something in return for benefits in other areas.

and finally, consequence is a general term used to accept what it comes when you make a decision. it can be a positive or negative consequence depending if the decision you took was the correct one.