◡AMB + ◡ANB = 360
◡AMB = 5x
◡ANB = 13x
5x + 13x = 360
18x = 360
x = 20
◡AMB = 5 * 20 = 100
∠AMB = 1/2 * ◡ANB = 1/2 * (360 - 100) = 1/2 * 260 = 130
Ответ: 130