The length of the line is B. 5
How to find the length of the line
The length of the line is solved using Pythagoras theorem, giving by the formula
hypotenuse² = adjacent² + opposite²
The line is the hypotenuse
hypotenuse² = 3² + 4²
hypotenuse² = 9 + 16
hypotenuse = √25
hypotenuse = 5 units