Parse based on '=' first, then parse based on '+' and '-' and then parse each split based on '*', then have 4 counters: SumLeftNums, SumLeftXs, SumRightNums, SumRightXs, and calculate the answer using the following equation: (SumLeftNums-SumRightNums)/(SumRightXs-SumLeftXs), just try to solve the equation in the question by hand, you will get all the clues, we could get fancy and have our own parse and split functions. Also we could use stack to calculate something similar to infix equation but it will get complicated.