Let the total number of friends in the dinner group = x
Let one contribution = y
Total contributions for gift = x * y = $36
Question: How many people are in the group? i.e we want to find the value of x.
From the contribution; xy = 36; x = 36/y
Statement 1: The number of people in the group is equal to the size of each person's contribution in dollar.
i.e x=y and y=x
From the calculation, xy = 36 (substitute y with x because y=x and x=y)
Therefore, x * x = 36 $$x^2=36,\ and\ x=\sqrt{36}=6$$
Based on this, state,emt 1 is SUFFICIENT.

Statement 2: If 3 more people joined the group, each person's individual contribution would fall by $2.
3 people joined the group => x + 3
Individual contribution => y - 2
Total contribution for gift = (x+3)(y-2) = $36
xy - 2x + 3y - 6 = 36
subsitute xy with 36 because xy=36 from the question stem
36 - 2x + 3y - 6 = 36
- 2x + 3y = 6
from xy=36; y=36/x
Therefore,
$$-2x+3\left(\frac{36}{x}\right)=6$$
$$-2x+\frac{108}{x}=6$$
$$-2x^2-6x+108=0$$
Divide through by -2
$$x^2+3x-54=0$$
(x - 6)(x + 9) = 0
x=6 or x=-9
Since contribution cannot be negative, then x=6.
Therefore, statement 2 is SUFFICIENT. Hence, each statement alone is sufficient, the correct answer is option D.