Because the area of triangular ADC = the area of triangular ADB (equal base and equal height)

So the area of triangle ADO+the area of triangle AOB = the area of triangle ADO+the area of triangle ODC.

Triangle area AOB = triangle area ODC = 15CM?

BO=2/3BD，DO= 1/3BD BO=2DO。

So the area of triangle ODC = 1/2 the area of triangle BOC.

Area of triangle BOC =2* area of triangle ODC =2* 15=30CM?

Area of triangle AOB =2* area of triangle AOD = 15.

The area of triangle AOD = 15/2=7.5CM?

Trapezoidal area = triangular AOB area+triangular ODC area+triangular AOD area+triangular BOC area.

= 15+ 15+7.5+30 = 67.5cm？