$300 for 13 years at 8% compounded semiannually. P=principle = original funds, r=rate, in percent, written as a decimal (1%=.01, 2%=.02,etc) , n=number of times per year, t= number of years

So we have:

$300 principal

13 * 2 = 26 periods for n

Rate r for a semiannual compound is 8%/2 = 4% per 6 month period