A= 12.8m
B=13.9m
C=12m
D= 7m

Answer:
C: 12m
Step-by-step explanation:
We can solve this by using the Pythagorean Theorem [tex]a^{2} + b^{2} = c^{2}[/tex]
For this triangle
a= x b= 5 c= 13
We now have the equation
[tex]x^{2} + 5^{2} =13^{2}[/tex]
If we simplify this we get
[tex]x^{2} + 25 = 169[/tex]
Next, we subtract 25 from both sides
[tex]x^{2} = 144[/tex]
Finally, if we take the square root of both sides of the equation, we find that
x= 12