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:

After doing the subtraction using a calculator or a pencil and paper, you get that:

So 171 years have passed from 1844 to reach to 2015.
Answer:
x+3= 2x when x = 3
3+3 = 2*3
6= 6
They are not equal when x is any other number rather than 3
1/3=2/6
-1/6= -1/6
then I guessing you add them?
2/6+-1/6=1/6