State whether the conjecture is true or false. if false, provide a counter example. subtraction of whole numbers is commutative

Which expression is equivalent to 8(k + m) − 15(2k + 5m)?

Gabrielle's age is two times mikhail's age. the sum of their ages is 84. what is mikhail's age?

Sam opened a money-market account that pays 3% simple interest. he started the account with $7,000 and made no further deposits. when he closed the account, he had earned $420 in interest. how long did he keep his account open?