1. The slope intercept form is:
Where 
is the slope of the line and 
is the intercept with the y-axis.
2. To calculate the slope, you can use the following formula:
Where:
3. So:
4. Now you must find . Substitute any of the given points into the equation and solve for :
5. Therefore, the answer is the last option:
The answer is 7×4=28 because 28÷4=7
What we know:
Lot= 21 x 30ft
Perimeter=2l+2w
Want to put 4 corner post and one post every 3 ft
What we need to find:
How many post we need.
Perimeter=2 (21)+2 (30)=42+60=102ft
102/3=34
34 posts are needed.
