(1,3) and (7,3) falls on the same horizontal line. hence, the distance is just equal to 6 units. (7,3) and (7,7) meanwhile lie on the same vertical line. hence the distance is 4. (7,7) and (4,7) lie on the same horizontal line with a distance of 3.
Finally, to get back to point (1,3) - (4,7) ----> (1,3), 3 to the left and 4 down, the diagonal being 5. 6+4+3+5= 10 + 8 = 18.
