Can someone please help I’m struggling

We just started the introduction into circles and i have no idea how to do this.

What is the probability of throwing several dice with sum equal to 6 (six)? show the ways of possibilities for sum 6 (as the numerator) and the ways of throwing n dices for n = 1, 2, 3, 4 or 5 as denominator for all the questions to earn full credits. (a)throw one die, (b) throw two dice, (c) throw three dice (d) throw 4 dice, (e) throw 5 dice

What is the missing reason in the proof? segment addition congruent segments theorem transitive property of equality subtraction property of equality?