Solution :
It is given in the question that Ben goes to the zoo by walking and then he walks down to the city park. He moves several blocks while walking from his home to the zoo and then to the city park.
The figure is provided below.
So from the picture, the least number of blocks that Ben had walked from his home to the city park can be found out by counting the number of blocks he moved.
So the least number of blocks will be = 19