N=9+x+y-z

Question

Where x,y,z are variable representation of some digit (0 to 9) Alok is like to maximize N while Bhanu Is like to minimize it towards this end ,Alok chooses a single digit number and bhanu substitute this for a variable of her choice (x,y or z)also chooses the next value and Bhanu , the variable to substitute the value .finally ALOK proposes the value for the remaining variable .assuming both playing to their optimal strategies,the value of N at the end of the game would be
a. 20 b. 0.0 c. 27 d. 18
also give description