Help me Also I have more of these sooo

The table shows the balance of a money market account over time. write a function that represents the balance y (in dollars) after t years.

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!

Find the greatest common factor of the followig monomials 21u^5v,3u^4v^6, and 3u^2v^5