I hope this helps you
q=24:4=6
b3=b1*q^2=4*6^2=140
b4=b1*q^3=4*6^3=816
2cos((П/9+П/13)/2)cos((П/9-П/13)/2)=2cos(22П/117)cos(4П/117)=
=2cos(0,19П)*cos(0,03П)
п=п*(180/п)