the sides of the triangles are,
AC = 7
CB = 18
AB = ?
AD = 6
from the law of triangle
the sum of the two sides should be more than the third side,
so,
AC + CB > AB
7 + 18 > AD +DB
25 > 6 + DB
subtract 6 from both side
25 - 6 > 6 + DB - 6
19 > DB
so, DB should be less than 19
now,
we take other two sides,
AC+AB > BC
7 + 6 +DB > 18
DB > 18 - 13
DB > 5
so DB should be greater than 5
thus, the answer is option B that is 12
