y=mx+b is the equation of a line;
m=slope , b= y-intercept
You can find the slope with this following equation: (y(2)-y(1))/(x(2)-x(1))
In this case the points are (0,4) and (-2,-3). The first set being (0,4) and the second (-2,-3). This means (0,4) can be expressed as (x(1),y(1)) and (-2,-3) expressed as (x(2),y(2)). Plugging these numbers into the slope equation gives us: (-3-4)/(-2-0) = -7/-2 = 7/2.
m= 7/2 ; so we have : y= (7/2)x+b
We are give a set of points which it passes through, we can simply plug them in:
4 = (7/2)(0)+b (0 is the x and 4 is the y)
We get 4 = 0 +b .... 4=b
our final equation is : y=(7/2)x+4