Mr. Mole's burrow was at an altitude of 6 meters below the ground.
Step-by-step explanation:
Step 1:
We need to determine the distance that Mr. Mole covers in a single minute.
To do that we divide the difference in values of altitude by the difference in the time periods.
For the first case, Mr. Mole had traveled -18 meters in 5 minutes.
We also have, he traveled -25.2 meters in 8 minutes.
Step 2:
The distance he covered in 1 minute 

So with every minute, Mr. Mole digs down an additional 2.4 meters below the surface.
To determine where Mr. Mole's burrow is we subtract the distance traveled in 5 minutes from -18.
The altitude of Mr. Mole's burrow 
So Mr. Mole's burrow was at an altitude of 6 meters below the ground i.e. -6 meters.
For this case we have to by definition, if two lines are perpendicular then the product of its slopes is -1.
That is to say:

We have the following equation:

So:

Thus:

Thus, a line perpendicular to the given line must have slope 
Option A:

It is not perpendicular!
Option B:

If it is perpendicular!
Option C:

It is not perpendicular!
Option D:

It is not perpendicular!
The correct option is option B
ANswer:
Option B
1/3x=20
1st step do the opposite of 1/3x to get it by itself. So you would do 1/3x *3/1 than you would do 3/1 *20. What you do to that side you do to the other.
2nd step 20*3=60
3rd You can check your answer by doing 1/3 *60=20
I plugged the answer in the variable to Check it
3.94314 this is the answer