Let numbers of books be 'b' and numbers of CDs be 'c'
We can set up two equations:
Equation [1] ⇒

Equation [2] ⇒

We are solving for the number of books and the number of CDs bought
When we have two equations in terms of two different variables;

and

, that we need to solve, then this becomes a simultaneous equation problem.
First, rearrange Equation [1] to make either

or

the subject:


Then we substitute

into Equation [2]






Now we know the value of

which is

, substitute this value into

we have

Answer:
Numbers of books = 13
Numbers of CDs = 7
It is possible to prove that the right triangles are congruent through the right angle hypotenuse side theorem.
Answer: 
Step-by-step explanation:
Vertical Angles states that 9x+27=117
Supplementary Angles states that 117+z=180
![9x+27=117\\Subtract (27)\\9x=90\\Divide(9)\\\left[\begin{array}{c}x=10\end{array}\right] \\\\117+z=180\\Subtract(117)\\\left[\begin{array}{c}z=63\end{array}\right]](https://tex.z-dn.net/?f=9x%2B27%3D117%5C%5CSubtract%20%2827%29%5C%5C9x%3D90%5C%5CDivide%289%29%5C%5C%5Cleft%5B%5Cbegin%7Barray%7D%7Bc%7Dx%3D10%5Cend%7Barray%7D%5Cright%5D%20%5C%5C%5C%5C117%2Bz%3D180%5C%5CSubtract%28117%29%5C%5C%5Cleft%5B%5Cbegin%7Barray%7D%7Bc%7Dz%3D63%5Cend%7Barray%7D%5Cright%5D)
<em>Hope it helps <3</em>