Resposta :
Erika,
Aplicando Teorema de Thales:
CM / MA = CN / NB
2x / 5 = (x + 4) / 8
2x(8) = 5(x + 4)
16x = 5x + 20
11x = 20
x = 20 / 11
CM = 2x = 2(20/11) = 40 / 11
CN = x + 4 = (40 /11 + 4) = (40/ 11 + 11 / 11) = 51 / 11
Ok??