The distance between gab's house and library will be 4km
What is Distance?
Distance is a numerical measurement  of how far apart object or point are or it may also refer as the physical length.
From graph we can see that Gabe's house is 3 km on positive x axis in respect to the origin
Whereas library is 1 km apart from origin on negative x axis
Since we are calculating distance , we simply add both the above mentioned distances irrespective of their direction since distance is a scaler quantity.
Distance between Gab's house and library will be :
