Y2-y1=m(x2-x1)
Y- (-3)=1/3(x-3)
In any trapezoid, the area is given by

where B and b are the two bases, and h is the height. You're given all these elements already, so you only need to plug the values in:

A rational number can be made into a fraction
0.21 = 21/100....so it is rational
A cube has 8
A square has 4
I think about 26.7
or something around there