PLS HELP ME I WILL MARK YOU BRAINLIST

Look at arnold's attempt to solve the equation for b: 3b = 12 b = 3 · 12 b = 36 describe the mistake that arnold made.

Math each whole number with a rational, exponential expression

Maria has $10,000 to invest in two accounts. he decides to invest one part in an account with 5% interest and the rest in an account with 8% interest. at the end of the year he has earned $702,50 in interest.¿how much did maria invest in the 8% account?