This is a subtraction machine. It subtracts seven from any number you put in. If we start with 14 and put 14 in the machine, seven will come out. 14 minus seven equals seven. If we put in the number 11 what number will come out?
Remember, the machine does subtraction. So we need to answer the question what is 11 minus seven. If you have 11 and you take seven away, the output will be four. 11 minus seven equals four. How about if we put 19 into the machine?
Our machine is doing subtraction. So we need to answer the question what is 19 minus seven. If we start with 19 and take seven away, we’ll be left with 12. The input on our subtraction machine is 19, the machine takes away seven and leaves us with 12. 11 minus seven equals four. 19 minus seven equals 12.