Summation of 2^n/n! with limit 1 to infinity

Which values for a and b will create infinitely many solutions for this system of equations? ax-y=8 2x+y=b

How do i do this? i don’t understand

Me! i really need to get this right before 9. prove the divisibility of 7^6+7^5-7^4 by 11. use factoring so you get a number times 11. just tell me the number. i need this done asap