What decimal value does the 8-bit binary number 10011110 have if?

Very simple:

10011110

1st Octet Value = 128

2nd Octet Value = 0 (64)

3rd Octet Value = 0 (32)

4th Octet Value = 16

5th Octet Value = 8

6th Octet Value = 4

7th Octet Value = 2

8th Octet Value = 0 (1)

so we add 128+16+8+4+2=158 and there is your Answer