i need help getting a number to display properly

im pretty new to unity and ive been trying to practice by making small programs to help with dnd, i wanted to make a number tracker where you can enter a number in and it will keep that number and then you can subtract from that number when you press a button, i cant not for a life of me get the subtraction working, ive look for hours on the web and tried countless t$$anonymous$$ngs and i cant figure it out, i need some help bad