Answer:

Step-by-step explanation:
Based off of what we do know, if we can find length DB we can use the pythagorous theorem (I will be assigning the variable z)

First equation is for triangle ABD
Second is for BCD
And the last one is for ACD
Substitute
and 

As discovered before

Use an app called Socratic, take a photo of the questions you're stuck on, then it will help you in stages and show you the answer.
Is this Long multiplication?
Answer:
3. is 3 (m - 16)(m + 4)
7. is also 3. (2x + 5)(3x - 5)
12. is 4 (x - 6)(x - 4)
the last one is i dont know