Looks like u got the answer from 1 of the 4 options in the question. but missing the mask wud change the story.
The summarised address should be 192.1.144.0 / 20
Lets calculate:
When 192.1.0.0 is subnetted, which subnet would consist of 159.2 & 151.254
The answer is: 192.1.144.0 / 20 since /20 includes 16 subnets each.
