Determine whether y varies directly with x. If so, find the constant of variation k and write the equation.

x y
4 6.4
7 11.2
10 16
13 20.8

Please show your work and give me an explanation. I have a test coming up and I am really stuck on these types of questions. I'd like to write this in my notebook for future reference and practice. :) Thanks! Will medal/fan as always.

Question

Determine whether y varies directly with x. If so, find the constant of variation k and write the equation. 

x       y   
4      6.4
7      11.2
10     16
13     20.8 

Please show your work and give me an explanation. I have a test coming up and I am really stuck on these types of questions. I'd like to write this in my notebook for future reference and practice. :) Thanks! Will medal/fan as always.