Step-by-step explanation:
Calculating the double bond equivalence as:
DBE = C - (H/2) - (X/2) + (N/2) +1
Where
C is the number of carbon atoms
N is the number of nitrogen atoms
X is the number of halogens
H is the number of hydrogen atoms
So, according to the formula, C₃H₆O,
DBE = 3 - (6/2) - (0/2) + (0/2) +1 = 1
It means there is one double bond and it is given in the question that it is not between the carbon.
It can be between oxygen and carbon or a ring.
The possible structures are shown in the image.