The four sides of the rectangle added together gives the perimeter.
The length of the sides is the following.
AD = 4, AB = 5, BC = 4, CD = 5.
After dilation by 1/2 each of the lengths above is multiplied by this factor; therefore, the lengths of the resulting rectangle is
A'D' = 4/2 = 2
A'B' = 5/2 = 2.5
B'C' = 4/2 = 2
C'D' = 5/2 =2.5
Hence, the perimeter of PQRS = A'B'C'D is
2 + 2.5 + 2 + 2.5 = 9