the form for a line is y=mx+b where m is the slope and b is the y intercept.
First off lets find the slope which you can think of as the rise over the run
(also the change in y value over the change in x value)
our first point is (0,6) and the second is (3,4), and we plug this into the equation
(4-6)/ (3-0) = -2/3
the slope is -2/3
now look at the graph. when the x value is 0, the y value is 6. This is the y intercept.
therefore your b is 6.
The answer is y= -2/3 x +6