Statement and reasons m< 1 +m< 2+ m< 3=180 whats the reason?

The correct answer for the question that is being presented above is this one: "the angles of a triangle sum to 180." m<1 +m<2+ m<3=180. The sum of all the angles of a triangle is 180. Since there are 3 angles that form part of a triangle, then the equation m<1 +m<2+ m<3=180  is how it represented it.

Idk what the answer is bc i don't get it