I would guess the answer to be Tension, if not for the extra 'X'....
or
Extension, if you add another 'E'...
Answer:
They encircle the planet
times.
Step-by-step explanation:
Consider the provided information.
We have 2.5 mole of dust particles and the Avogadro's number is 
Thus, the number of dust particles is:

Diameter of a dust particles is 10μm and the circumference of earth is 40,076 km.
Convert the measurement in meters.
Diameter: 
If we line up the particles the distance they could cover is:

Circumference in meters:

Therefore,

Hence, they encircle the planet
times.
Answer: y = 3x + 60
<u>Step-by-step explanation:</u>
Set up two equations and solve the system:
270 = 70x + b
- <u>(150 = 30x + b)</u>
120 = 40x
3 = x
Input "x" into one of the equations and solve for "b":
150 = 30x + b
150 = 30(3) + b
150 = 90 + b
60 = b
Equation: y = 3x + 60
This means that there is a flat fee of $60 plus a rate of $3 per student