Let c=amount invested in C o D, then 170000-c is invested in AA bonds.
So 0.05c+0.11(170000-c)=15700.
0.05c+18700-0.11c=15700
3000=0.06c
c=3000/0.06=300000/6=50000.
C o D investment=$50,000 and AA investment=$120,000.
CHECK
0.05 of $50000=$2,500; 0.11 of $120000=$13,200; 2,500+13,200=$15,700.