We start to solve this by looking for the formula that let us calculate an average value, this formula would be:

where Save is the average score and s is the score of each exam, Since we know the value of the score Save and 4 of the exams we can replace them in the formula, like this:
And we can solve for s5, which is the score that we need to find, like this:

Then, Pedro must have a 55 score on the fifth test
Answer:
B (I think)
Step-by-step explanation:
I believe it's B, sorry if I'm wrong.
If you're looking for the decimal it is
0.71428571428
The function representing the price of the ring x years after 2000 is f(x) = (100 + 35)/100 *x + 590 = 135/100 *x + 590 = 1.35x + 590
i.e. f(x) = 1.35x + 590