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 ?