Remember that
The compound interest formula is equal to

where
A is the Final Investment Value
P is the Principal amount of money to be invested
r is the rate of interest in decimal
t is Number of Time Periods
n is the number of times interest is compounded per year
in this problem we have
P=$3,200
r=5 1/2 %=5.5%=0.055
t=6 years
n=2
substitute the given values

A=$4,431.31 ------> the total
Find out the interest
I=A-P
I=4,431.31-3,200
I=$1,231.31 -----> interest