Answer:
8+2x and 3(x+4)-(4+x)
Step-by-step explanation:
2(x+4)=2x+8 interchanged to 8+2x
3(x+4)-(4+x) simplified to
3x+12-4-x collect like terms together 3x-x+12-4=2x+8
Answer:
15,240,960 serial numbers
Step-by-step explanation:
Since no repeats are allowed and the order matters, the number of possible serial numbers is given by the product of the permutation of 4 out of 9 letters by the permutation of 4 out of 10 numbers:

There are 15,240,960 ways to generate a serial number.