Which expression demonstrates the use of the commutative property of addition in the first step of simplifying the expression (–1 + i) + (21 + 5i)? (–1 + i) + (21 + 5i) + 0 –1 + (i + 21) + 5i (–1 + 21) + (i + 5i) –(1 – i) + (21 + 5i)

Delbert keeps track of total of the total number of points he earns on homework assignments, each of which is worth 60 points. at the end of the semester he has 810 points. write an equation for delbert’s average homework score a in terms of the number of assignments n.