2х+5х+7х+4х=360°

18х=360°

х=360°/2

х=20°

2х=2*20=40°

5х=5*20=100°

7х=7*20=140°

4х=4*20=80°

делаем проверку:

40°+100°+140°+80°=360°

360°=360°