Answer:
paper clips = $1.85
index cards = $3.95
Step-by-step explanation:
Mark
12 paper clips = x
10 index cards = y
$61.70 total
Janice
15 paper clips = x
7 index cards = y
$55.40 total
12x + 10y = 61.70
15x + 7y   = 55.40
*** you want to cancel out one of the letters
(12x + 10y = 61.70) * -7
(15x + 7y   = 55.40) * 10
-84x -70y = -431.9
150x + 70y = 554.0
150x + 70y = 554.0
-84x -70y = -431.9
66x + 0 = 122.1
66x = 122.1
x = 122.1 ÷ 66
x = 1.85
plug it back in
15(1.85) + 7y   = 55.40
27.75 + 7y   = 55.40
7y   = 55.40 - 27.75
7y = 27.65
y = 27.65 ÷ 7
y = 3.95
 
        
             
        
        
        
Since the graph is a linear function, we're going to use the slope formula solve this: 
Note I am replacing m with k

Inserting 2 points from the graph, let's use (1,8) and (2,16).

k=8
 
        
        
        
Use the interior angles theorem for the triangles I hope my answer helped if you have any questions don't be afraid to ask <span>(o^▽^o) <3</span>
        
                    
             
        
        
        
Perimeter is the sum of all the sides of the shape
do you know the length of each side of the parallelogram?
        
                    
             
        
        
        
They give us the length of side of the square which is 3-7x.
To get an expression for the perimeter that is expressed as a product we have to multiply the expression 3-7x by four since every square has four sides. This will give us an expression of 4(3-7x). We than can use the distributive property to multiply everything inside the parenthesis by 4. This will give us an expression of 12-28x.