Answer
$A_{80}\ne 2\times A_{40}$
Work Step by Step
$A_n=10,000(1+\frac{0.035}{4})^n$
In order to find the balance after 20 years we need to compute the 80th term of the sequence:
$A_{80}=10,000(1+\frac{0.035}{4})^{80}=10,000(1.00875)^{80}=20076.31$
From item (b):
$A_{40}=14,169.09$
It is clear that $A_{80}\ne 2\times A_{40}=28,338.18$
