Help Me With This Question Please

Explain how you can use the triangle sum theorem to find the measures of the angles in an equilateral triangle. the angles of an equilateral triangle are . let the measure of each angle be x. then, by the triangle sum theorem, x + x + x = 3x = ° solving for x gives x = °

Ineed i do not understand i'm only 8

What is the standard form of -5x^2+2x^4-11+x^3+3x