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.
I believe that the slope would be 4/2 or 2, but i wouldn’t take my word for it
The Cricket. because it measures 1 inch, and all the others are less that one inch.