SOLUTION
From the question given the following statements to prove are correct, then the last part

The reason is Side-side-side triangle theorem
This theorem states that all three sides of a triangle are congruent (identical) to the corresponding sides of another triangle, then the triangles themselves are also congruent.
Hence the answer is Side-side-side triangle theorem
The answer to question seven and question nine is
Answer: 72
<u>Step-by-step explanation:</u>
There are 9 students to choose from to go the library. After that person is chosen there are 8 students remaining.
First student and Second student
9 x 8 = 72