What is the largest decimal value that can be represented with – c

 
What is the largest decimal value that can be represented with (hint – can use calculator) (20 points)
(Note : 1 byte = 8 bits)  

What is the largest decimal value that can be represented with 15 bits?
What is the largest decimal value that can be represented with  4 bytes
What is the largest decimal value that can be represented with  7 bits
What is the largest decimal value that can be represented with 25 bits

please show work