Andrew is trying to create a number puzzle for his younger sister to solve. He challenges his sister to find the mystery number. “When is 8 subtracted from half number of a number, the result is 10” the equation to represent the mystery number is 1/2x - 8 = 10 , Andrews sister tries to guess the mystery number. Andrews sister makes three guesses to what the answer is. She guesses. 4, 18 and 36. Which one is correct ?