Answer:
AD = 3
Step-by-step explanation:
Pythagoras theorem formula: a² + b² = c² (c being the hypotenuse, the longest side of the triangle).
Using this formula, you can easily say that c²-b²=a². c=5, b=4, making the equation 5² - 4² = a ².
Expanding the formula, you'll get 25 - 16 = a².
25 - 16 = 9. 
This means that 9 = a².
To find a, you need to root 9. Using a calculator, you'll know that this number is 3, meaning that AD = 3.
 
        
             
        
        
        
okay... THE ANS IS 5/35 IS THE RIGHT ONE
 
        
             
        
        
        
Answer:
Step-by-step explanation:
Multiplying Equation A by (1/3) and adding the result to Equation B will do the trick.  Let's actually solve the problem!
Equation A:  (5/3)x + 3y = 12
Equation B:    4x     -  3y = 8
                     ---------------------------
                      (5/3 + 12/3)x = 15        Note how this has eliminated the variable
                             (17/3)x = 15           y.
                                    x = (3/17)(15)