how do you find value of the constant ?

According to the graph, what is the value of the constant in the equation below?

(picture) http://i.imgur.com/9F8y6N2.png

Question

how do you find value of the constant ? 

According to the graph, what is the value of the constant in the equation below? 

(picture) http://i.imgur.com/9F8y6N2.png

imstuck · Answer

To find the value of the constant, find the rate of change between the values.  That is also known as the slope.  The difference in the y values over the difference in the x values gives you this constant.  Just FYI, it is 1.5   Try it.

anonymous · Answer

can you give me a formula?