Answer:
<h3>a.

</h3>

<h3>b. Your friend is wrong.</h3>
Step-by-step explanation:
If you begin with $90 and add $10 each week, then we express it as

Where
refers to weeks and
refers to the total amount of money in you savings account.
On the other hand, your friend begins with $35 and deposits $15 each week, the equation that expresses your friend's savings is

Therefore, the sytem of linear equation that models this situation is


The graph attached shows this system. There you can notice that the solution is (11, 200), which means in 11 weeks both will have the same amount saved.
Therefore, your friend is wrong, because after 10 weeks you won't have the same amount.