Step-by-step explanation:
we need to use pythagoras's theorem (reversed) in this situation. We know the hypotenuse and the lower line, so we can find the upright one. That will be the value of AD.
so we use 81 (9 squared) and 144 (12 squared)
let x be the upright line's length
144-81=x squared
63=x squared
find the square root of 63 and you can have your answer
Im not gonna do that for you because that's pretty easy
