Answer:
40 ft²
Step-by-step explanation:
Let the length of the original rectangle be L and original Breadth be B
it is given that the original area  is 5/8 ft²
i.e.
Original Length x Original Breadth = Original Area, or, 
LB = 5/8 ft² ------------------(1)
Given that the dilation factor is 8, 
Hence, 
New Length = 8L and New Breadth = 8B
THerefore, 
New Area = 8L x 8B
= 64 LB  (from (1) above , we know that LB = 5/8 ft², substitute into expression)
= 64 (5/8)
= 40 ft²