Find the x and explain how you found it

In the rectangle below ac=30 units what is de

For the equations below which statement is true ?

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!