Prove that EF is parallel to AB and CD in part (iii) using intercept theorum?

Dear student,
I am giving a solution for c first part as your question is not clear and for the remaining parts kindly ask in another thread

$$\begin{gathered} We know that the length of the line segment joining the mid-points of \\ two non-parallel sides is half the sum of the lengths of parallel sides. \\ \because E and F are mid-points of AD and BC. \\ \therefore EF= \frac{1}{2} (AB+CD) \\ Now, given that- \\ AB=6cm \\ DC=4cm \\ \therefore EF=\frac{1}{2} (6+4)=5cm. \end{gathered}$$