10. (10%) There are some red and white balls in a basket. Now we randomly select one ball from the basket with replacement until we obtain a red ball. Let Xi be the number of balls we select from the basket before we get the red ball. The whole process is repeated for n times, which means that we can have ( X1, X2, X3......., Xn) as a sample. Please use MLE to find out the estimator of the ratio R, where