H. W Exercise 8. Prove that a ring (R,+..) is commutative if and only if (a+b)2 = a + 2(a.b) + b, for all a, b ER. 11. Austin Blake borrowed $12,000 on a 11% 240-day note. On the 90th day, he paid $3,800 on the note. If ordinary interest is applied, what is Austin's adjusted balance due at maturity? $8,920.96 $3,470 $8,530 $8,200 (12. What is the effective interest rate of a simple discount note for $10,000 at an ordinary bank discount rate of 9%, for 120 days? Round to the nearest tenth percent. 9% 9.3% $300 1.0%