Answer:
x = 25
Step-by-step explanation:
The three straight lines in the sides of the triangle means that ALL 3 SIDES ARE EQUAL.
This is an equilateral triangle. So all 3 angles are equal.
We know sum of 3 angles in a triangle is 180. Since 3 of the angles are equal, each angle is:
180/3 = 60
The top angle is given as "2x + 10", thus we can say "2x + 10" is equal to 60 degrees. Now we equate and solve for x:

The value of x is 25
Answer:
C. postulate; theorem
Step-by-step explanation:
While a "given" is taken as true without proof, and a "problem" sometimes involves an assertion that can be proven, the answer choices involving these terms are not correct here.
The dictionary definitions of "postulate" and "theorem" apply. It is useful to learn the meaning of these terms so you can understand problems and descriptions that use them.