Answer: The exact answer is 3.61 weeks, so the "about" answer is 4 weeks.
Explanation:
b = $85 + w (10+8)
b = 85 + w (18)
b = 85 + 18w
b is the total amount need in the bank account, so $150.
$150 = $85 + 18w
$150 - $85 = $85 - $85 + 18w
$65 = 18w
$65 / 18 = 18w / 18
3.611 weeks = w
So, it will take about 4 weeks to get $150 in his bank account.
Hope this helps!