The first one is the answer because he starts with $300 (which would be the b in this case) and he gets $5 for EACH customer (so that would be 5x)
Answer:
See the proof below.
Step-by-step explanation:
For this case we need to proof the following indentity:

So we need to begin with the definition of tangent, we know that
and we can do this:
(1)
We also have the following identities:


Now we can apply those identities into equation (1) like this:
(2)
We can divide numerator and denominator from expression (2) by
we got this:

And simplifying we got:

And that complete the proof.
2 + 7 + 2 + 7 + 2 + 7 + 2 + 7 + 2 + 7 = 45
7 = 5 + 2
10 weeks
they have been saving their money for 10 weeks