Bài giải:

${{S}_{AMN}}=\frac{2}{3}\times {{S}_{NAB}}=\frac{2}{3}\times \frac{1}{3}\times {{S}_{ABC}}=\frac{2}{9}\times {{S}_{ABC}}=40\left( c{{m}^{2}} \right)$

${{S}_{BMQ}}=\frac{1}{2}\times {{S}_{MBC}}=\frac{1}{2}\times \frac{1}{3}\times {{S}_{ABC}}=\frac{1}{6}\times {{S}_{ABC}}=30\left( c{{m}^{2}} \right)$

${{S}_{CPQ}}=\frac{1}{2}\times {{S}_{PBC}}=\frac{1}{2}\times \frac{1}{3}\times {{S}_{ABC}}=\frac{1}{6}\times {{S}_{ABC}}=30\left( c{{m}^{2}} \right)$

${{S}_{MNPQ}}=180-40-30-30=80\left( c{{m}^{2}} \right)$

    Đáp số: 80cm²