The answer is C.
If you multiply the top equation by 3 the x variable would become 2x * 3 = 6x
Multiplying the second equation by 2 the x variable becomes -3x * 2 = -6x
You would then have 6x - 6x, which would eliminate the x variable.
It would be 0.06 so 6 cents
Let a and b be integers and b>a, then we can say:
(b-a)/3=5 now multiply both sides by 3
b-a=15
b=15+a
So there are infinitely many pairs of integers that satisfy the conditions given in the problem. For any value a, b will be 15 units greater.
Remember that the rule with multiplying exponents with the same base is to add the exponents together.
In this case: 
10^12 is your answer.
