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10-8.

What if Uncle Zachary (from problem 10‑1) had increased the amount he was saving for Angela by $5$ each month instead of $3$?

1. How much would Uncle Zachary have deposited on Angela’s second birthday?

Recall that Uncle Zachary puts $50$ in Angela's account the first month.
In this case he will put $55$ in Angela's account the second month and $60$ the third month.

The sequence is $50, 55, 60, 65, ...$, which is linear. The equation should be of the form $an + b$.

2. Write a formula for the $n$th term of the sequence for this situation.

$t\left(n\right) = 50 +5\left(n − 1\right)$ or $t\left(n\right) = 5n + 45$

3. How much money would have been in the account on Angela’s first birthday, just after Uncle Zachary made his $12$th deposit?

Add the first $12$ terms of your sequence.