Add the three angles and set them to 180
4x-13+15+x+18=180
5x+20=180
5x=160
x=32
Then plug in to get A and C
A=4*32-13 
A=115
C=32+18
C=50
        
             
        
        
        
<u>5x² + 9x - 1</u><u> is  the expression that represents a </u><u>quadratic expression</u><u>.</u>
What is  quadratic expression?
- Quadratic expression is an expression with the variable with the highest power of 2.
-  The word quadratic is derived from the word quad which means square. 
- The expression should have the power of two and not higher or lower.
A quadratic expression is of the form
ax² + bx +c = 0                    where a ≠ 0
The give options are-
9x - 2 
5x² + 9x - 1
-2x³ + 8x² - 7x +1

From the given options, the only expression which is quadratic is
5x² + 9x - 1
wChoose the expression that represents a quadratic expression. 9x − 2 5x2 9x − 1 −2x3 8x2 − 7x 1 x4 − 12x3 8x2 −here a =5, b=9 and c=-1
Therefore, 5x² + 9x - 1 is  the expression that represents a quadratic expression.
Learn more about  quadratic expression.
brainly.com/question/24108537
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Answer:Volume = 108 cm ³
Explanation:For a square pyramid, the volume can be calculated as follows:
Volume = 

 * area of base * height
Volume = 

 * side² * height
We have:
side length = 6 cm
height = 9 cm
Therefore:
Volume = 

 * 36 * 9 = 108 cm ³
Hope this helps :)
 
        
             
        
        
        
500 songs in his music player: + 500
every week he adds 10 songs: 10n (n is how many weeks) 
equation: s = 10n + 500 (s is the total amount of songs)
after 20 weeks? : plug it in
s = (10 x 20) + 500
s = 200 + 500
s = 700
he will have 700 songs in his music player after 20 weeks