The middle question my sister needs and i don't know how to solve it

Which addition property is being illustrated below? (type commutative or associative) (6 + 7) + 1 = 6 + (7 + 1)

Two customers went to a post office. first customer paid $12 for 14 and 5 envelopes the second paid 24.80 for 10 postcards and 15 envelopes. what is cost of each envelope?

2pointswhich of the following appear in the diagram below? check all that apply.d a. zcdeов. сеo c. aéo d. zdce