Question

What is number 3

Answer 1

Here's the paper

Answer 2

Since you are given choices, have you examined all possible choices, and make sure you understand all of them?

Answer 3

Number 3 is Given

Answer 4

6+10 = 16 which L = 16

Answer 5

JL+LK=JK is a statement related to general line segments, not specific for this case of 6+10=16.
If the statement is general, your justification is also general.
Please examine and understand each and all of the answer options before making a choice. This is the chance for you to learn and check your understanding, which is the purpose of the exercise.