Answer:
You are building your kids a small desk, where the width is 1/3 of its length. The length of the desk is 6 feet. What is it’s width? What is the area of the desk?
First you differentiate to find the gradient
dy/dx = (6 - - 8) / (-4 - 7)
= 14 / -11
= - 14/11
Then you use this formula
y - y1 = m (x - x1)
y1 being the y coordinate
x1 being the x coordinate
m being the gradient (or slope)
y - 6 = -14/11 (x - - 4)
y - 6 = -14/11x - 56/11
y = -14/11x + 10/11
So,

Distribute.
2 - p + 2p = 12
Simplify.
2 + p = 12
Subtract 2 from both sides.
p = 10
The correct answer is D.