Question

find out the binary substraction by using binary complemetry method 10011101 from 11101000

Answer 1

If I understand correctly, you are looking for 11101000-10011101 using the complementary method.
Well,
11101000
+01100010 (since 10011101+01100010=11111111)
+ 1
_________
101001011
now, subtract 100000000 making your answer 01001011

Basically what you are doing is adding a specific number (the radix I believe) to make the subtraction process easier.

To check our answer, we can convert back to decimal so:
11101000 = 232
-01100010 = -157
______________
01001011 = 75

If it helps, this is how the process looks when you convert all the numbers to decimal first and then use the complementary method:

232
+ 98
+ 1
______
331
- 256
_____
75