hosts - how to write extend network prefix? -

I need help with this:

Assume that you have been assigned the network 200.35.1.0 / 24 block Define an expanded network prefix that allows to create 20 hosts on each subnet.

I have written the addresses in binary form: IP: 1100 1000 0010 0011 0000 0001 0000 0000 Mask: 1111 1111 1111 1111 1111 1111 0000 0000

Expanded network prefix should be: < / P>

New mask: 1111 1111 1111 1111 1111 1111 Xxxx xxxx

I know that 2 ^ value - 2 = subnets
but how do you know how much of it is needed? Subtitles are not provided .. Help?

1. 2 is the next largest power of 2 of the required 20 hosts.
2. 32 2 ^ 5
3. There are 32 bits in an address or mask.
4. 32 bits for mask size - 5 bit = 27 bits mask length for subnet size
5. A 27-bit mask 11111111.11111111.11111111.11100000
6. Take the original subnet
7. 32 for each novel
8. Change the binary back to decimal

/ Div>