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°
