∠АКВ=180-125=55°
∠АВК=180-30-55=95°
∠КВС=180-95=85°
∠DKE=180-125=55°
∠KDE=180-55-20=105°
∠KDC=180-105=75°
∠C=360-125-95-75=75°

или можно короче:
∠АКВ=180-125=55°
∠АВК=180-30-55=95°
∠КВС=180-95=85°
∠С=180-20-85=75°