Question 539948
The equation you need to solve this problem is:
{{{x=p*((1+i)^n)}}}
Where:
x = the final resulting sum of money
p = original principal
i = interest rate of the compounding period
n = number of compounding periods
.
.
P is given in the problem.
{{{p=15000}}}
To calculate i, you should take the annual rate and adjust it to the semiannual rate (semiannual meaning twice per year), by dividing by 2.
{{{i=.046/2=.023}}}
Likewise, adjust the timeframe to find the number of compounding periods. 
{{{n=11*2=22}}}
Then, just plug in your figures into the equation.
{{{x=15000*((1+.023)^22)=15000*1.694164=24737.47}}}
After 11 years of semiannual compounding, the $15,000 will grow to $24,737.47.