Hello I need help on this math question

Divide: 1573 ÷ 7 = a) 222 r5 b) 223 r6 c) 224 r5 d) 224 r3

Using pert, adam munson was able to determine that the expected project completion time for the construction of a pleasure yacht is 21 months, and the project variance is 4. a) what is the probability that the project will be completed in 17 months? b) what is the probability that the project will be completed in 20 months? c) what is the probability that the project will be completed in 23 months? d) what is the probability that the project will be completed in 25 months? e) what is the due date that yields a 95% chance of completion?

Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9