a 4000 pound car driving at 40 miles/hour has time the kinetic energy of another 4000 pound car driving at 10 miles/hour

Ineed to know the answer to this algebra question.

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

Pamela has a 30-year, 5.75% mortgage on her $250,000 home. she has been paying on it for 5 years, and has recently hit some financial trouble. if her lender agreed to lower the interest rate on her $231,905.47 balance to 5.5%, what will her new payment be for the remainder of the loan?