How do i know when to divide multiply add or subtract in a math word problem

2(n-1)+4n=2(3n-1)n=0no solutioninfinitely many solutions n= - 4 !

Which expression gives the area of the triangle shown below

Asocial networking site currently has 400,000 active members, and that figure is predicted to increase by 32% each year. the following expression represents the number of active members on the site after t years.