To find the number of years between 1844 to 2015 you have to subtract.
Lets say that x is the # of years in between 1844 and 2015
Then we have:
\(\sf{2015 - 1844 =x}\)
After doing the subtraction using a calculator or a pencil and paper, you get that:
\(\huge{\boxed{\bf{x=171}}}\)
So 171 years have passed from 1844 to reach to 2015.
