Answer:
255.255.255.192
Explanation:
Given subnet : 192.168.31.0/26
This implies that there are 26 1-bits in the subnet mask. So the subnet mask is:
11111111.11111111.11111111.11000000 (26 1's)
Translating each segment into decimal representation:
11111111 = 2^7 + 2^6+2^5+2^4+2^3+2^2+2^1+2^0
= 128+64+32+16+8+4+2+1
= 255
11000000 = 2^7 + 2^6
= 128 + 64
= 192
So the overall subnet mask is : 255.255.255.192
