Answer:
Third option. 
Step-by-step explanation:
For this exercise you need to remember one of the properties for exponents.
There is a property called the "Negative property of exponents" which states the following:
Where 
As you can observe,
is the reciprocal of 
In this case you have the following expression given in the exercise:

Observe the expression. As you can notice, the base "n" has a negative exponent, which is -6.
Therefore, applying the Negative property of exponents explained at the beginning of this explanation, you can simplify the expression.
Then, the simplified form of
is the one shown below:

Hmmm i want to say 12 because it says "each dollar he spends on a candy bar:
Total cost = 15*14 ( 0.89 + 2.99 ) + 2(15 + 14) 0.19 = $825.82
Bud $100 - $50 Donation = $50
17 Students at a $3 Profit per student gives you $51 covering the cost of the Bus and also covering the $7 cost per student.