assume your salary was $30,000 in 2010 and $40,000 in 2012. if your salary follows a linear growth pattern, what will your salary be in 2015?

With the given info it would be +5,000 every year leaving you with 55,000 as the answer

2019 - 2016 = 3 years.
30,000 * 1.08^3 = 37,791.36.
because of inflation, if something cost 30,000 today, it will cost 37,791.36 three years from now.
in order to pay for that same things three years from now, you need to be making 37,791.36 dollars.
your salary needs to grow by 8% a year just to keep up with inflation.
if you make less, you lose buying power.
if you make more, you gain buying power.