1. Your expression is correct, I got 17720.35
(this might seem high, but true. Back in the "olden days" before calculators we used something called the rule of 72. It meant if you have a time and rate which multiplied to something close to 72, your money would double.
e.g. at 8% money would double in appr 9 years (9x8=72)
e.g. 100(1.08)^9 = 199.90
in your case it would have doubled in 8 years to appr. 11560 , which would reach 23120 after 18 years.
So 17720 after 13 years is reasonable.
2. amount = 3500(1 + .05/2)^(9(2))
= 3500(1.025)^18 = 5458.81
3. your expression is correct again, perhaps you don't know how to use your calculator
the magic key is the yx key
e.g. to do 4^3
press the yx key
you should get 64
so for A = 1200(1+.07/12)^216
here are my keystrokes
= -------> at this point you should have 3.5125...
you should get 12293.89
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