Acarpenter cuts of from a plank 5/12 of its length and then 6/7 of what remains. of the remaining piece is 2/1/2 m long. find the original length of the plank

Dakota earned $7.50 in interest in account a and $18.75 in interest in account b after 15 months. if the simple interest rate is 4% for account a and 5% for account b, which account has the greater principal? explain. to make it a little easier, there is an image. good luck!