What is the length of mn

Answer:
Option a)4
Step-by-step explanation:
Given is a triangle LMN with angle L = angle N
Hence this is an isosceles triangle.
So two sides opposite two congruent angles would be equal
i.e. [tex]4x=x+3\\4x-x=3\\3x=3\\x=1[/tex]
MN = 1+3 =4
So answer is option A) 4