Which equation are you talking about
I don’t see the pic !
Given that triangle ABC is right angle triangle. CD is altitude such that AD=BC
ABC is a right angle triangle so apply Pythogorean theorem

(Given that AD = BC)
(Given that AB=3)
...(i)
ADC is a right angle triangle so apply Pythogorean theorem



...(ii)
Plug value (ii) into (i)





Hence final answer is 
Answer:
x=23
Step-by-step explanation:
A and D are equal to eachother so you write the equation (x-4)=19. To solve all you have to do is add 4 to each side and you will get the answer of x=23