The quadrilateral ABCD was dilated by a scale factor of 3/4 to form the quadrilateral A'B'C'D'
This means that each side of the quadrilateral was multiplied by 3/4 to make the dilation.
You know that the scale factor is 3/4 and the length of D'A' is equal to 30 units, then:
![\begin{gathered} D^(\prime)A^(\prime)=(3)/(4)DA \\ 30=(3)/(4)DA \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/viuk7enq9k0ui8pfbgw2184axnkzo6zxol.png)
Multiply both sides by the reciprocal of 3/4
![\begin{gathered} 30\cdot(4)/(3)=((4)/(3)\cdot(3)/(4))DA \\ 40=DA \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/bvb46ez4h3c9i8ixmlgd6fa1umnd708drj.png)
The length of side DA is 40 units.