Idk what it means, sorry and good luck
        
                    
             
        
        
        
84 x .70 = $58.80
Or if you want to do it the long way you can calculate the actual discount (your savings from this purchase first then subtract it from the original price of $84. It`s just easier to figure out what is left (which is 70% of $84).
        
             
        
        
        

Above, I changed the fraction form of x and y into exponential form so it is easier to see the differentiation. Now, we can differentiate:

Now that we have dy/dx, we can plug in the x, which is 4, and the y, which is 4/19. We know these values of x and y because your question stated y(4) = 4/19.
 
 
        
             
        
        
        
This is the answer in exact form
 
        
        
        
<u>Final Answer:</u>
x = 20
<u>Step-by-step explanation:</u>
we'll be using the pythagorean theorem method, in this triangle the missing letter is a.
formula: 
a = x
b = 21
c = 29
a = 
a =  (note: 29² = 29 × 29 = 841 and 21² = 21 × 21 = 441)
     (note: 29² = 29 × 29 = 841 and 21² = 21 × 21 = 441)
a = 
a = 20
x = 20