This is combination problem since the order or arrangement matters. This is easily solvable with your scientific calculator. The formula would be nCr, where n is the total number of persons, and r is the number of persons in a group. So, using your calculator,
7C3 = 35
There can be 35 different groups.
If you need to simplify the equation it would be:

+2r-2n+7
If not sorry..
Hope This Helps!
The most appropriate choice for equilateral triangle will be given by
Value of x = 
What is equilateral triangle?
A closed two dimensional figure with three sides and three angles is called triangle.
Based on sides of triangle, triangle can be classified as equilateral, isosceles and scalene
The triangle whose all sides and all angles are equal is called equilateral triangle. All the angles of equilateral triangle are 60°
Here,
Since the triangle is equilateral, angle of triangle is 60°
sin 60° = 
= 

To learn more about equilateral triangle, refer to the link:
brainly.com/question/2351368
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The answer is the second one. [ Step 1 : 27x - 18 = 1 Step 2 : 27x = 19 ]