Maths

you know the formula: A = P times (1 + r/100)^n
where
A=current $$
P=amount of $$ in bank
r= 年利率
n= number of years (or in this case, half a year)

using the formula..solve for r:
37110 = 3200 x (1+r/100)^6
37110/3200 = (1+ r/100)^6

6√37110/3200 = 1+ r/100
1.50449297... - 1 = r/100
r = 0.50449297 * 100
=50.449297

hope it helps!
(sorry for the bad formatting..!)

A=P(1+r/100)^n
37110=3200(1+r%/2)^(2*3)
r=100.9

因為半年複利一次，所以利率需要除以2, 然後需要2次方
即:
3200[1 + r%/2]^[(3)(2)] = 37110
　　　　[1 + r/200]^6 = 3711/320
　　　[(200 + r)/200]^6 = 3711/320
　　　　　(200 + r)^6 = (3711/320)(200)^6
　　　　　　　200 + r = 300.8986
　　　　　　　　　　r = 100.8986