Make the trapezoid into a rectangle and two triangles, so that the rectangle is sandwiched between the triangles. If x=length of the base of one triangles, the length of the base of the other is 9-x.
Area of rectangle=base * height=shorter side * height=5*4=20 sq in.
Area of one triangle=(1/2)base*height=(1/2)x*4=2x.
Area of other triangle=(1/2)(9-x)4=2(9-x)=18-2x.
Add the areas together: 20+2x+18-2x=38 sq in.