Answer:
The answer is D.
Step-by-step explanation:
First, you have to find the differences in number of guests in this 2 party :
[tex]31 - 20 = 11 \: guests[/tex]
Next, you have to divide by the smaller value which is the first party, then, multiply by 100 as the question wants percentage increase :
[tex] \frac{11}{20} \times 100 = 55\%[/tex]