I am assuming both are six-sided and have numbers 1-6 on each of the six sides. There are 36 possible roll combinations. Of the 36, four result in 9 and six result in 7. Therefore there is a 10/36 chance of rolling a 7 or a 9. That can be simplified however by dividing by two on both numbers. That equals 5/18. As a percent you would divide 5 by 18 and get 0.2777. After that you multiply 0.2777 by 100 to get 27.77%.
