Hi Gina,
You are close. The formula you listed is the formula to find the slope of the line. By plugging in values from the two points, it becomes:
5  2 7
 = 
0  4 4
So, 7/4 is the slope of the line. Recall that the slopeintercept form is y = mx + b, where m is the slope, and b is the yintercept. So now that you know the slope, you have:
y = 7/4x + b
To find b, use either of your two given points and plug the x and y values into your equation. Lets use (4,2), so x is 4 and y is 2:
y = 7/4x + b
2 = 7/4(4) + b
2 = 7 + b
5 = b
So the final equation is:
y = 7/4x  5
Double check by plugging in values from your second given point, (0, 5):
5 = 7/4(0)  5
5 = 5
12/16/2013

Kevin F.