Michael has a substantial student debt, but he recently got a new job, which came with a signing bonus. He calculates that with his new job, he can put aside a fixed amount of money every month to pay off his debt. He also puts the entirety of his bonus towards paying off his debt. He constructs the expression 35500 - ( 6000 + 600m ) to represent the size of his debt after m months. Which number describes the value of his signing bonus?