∠A+∠B+∠C+∠H=360°1
∠H+∠H'=180°2
∠H'+∠G+∠F+∠S=360°3
∠S=∠D+∠E 4
4带入3得:
∠H'+∠G+∠F+∠D+∠E=360°5
5-2+1便得答案.540°