CSC cp7 practice calculating the fair price of bond

sarifa is considering inversting in an 8%, $1000 par value…..
N=5*2=10
IY=6%/2=3%
PMT=(8%/2)*100=4
FV=1000
PV=?
通过计算器计算得出=-778.2147
公式得出=28.079+789.409=817.488
都和答案不符 
具体哪里算错了呢？