Step-by-step explanation:
x = mass of apples
y = mass of strawberries
z = mass of the box
x = 3y
x + z = 16240
y + z = 6350
let's subtract the second from the first equation
 x + z = 16240
- y + z = 6350
-----------------------
x - y + 0 = 9890
using the first identity in that result gives us
3y - y = 9890
2y = 9890
y = 4,945 g
x = 3y = 3×4945 = 14,835 g = the mass of the apples
 
        
             
        
        
        
350 x 3/7= 150
There are 160 boys who attend the school.
        
             
        
        
        
A ) The domain:

x ≤ -4  and x≥ 4  or:  x ∈ ( - ∞ , - 4 ) ∪ ( 4  , + ∞ )
b ) f ` ( x ) = 

c ) The slope of the line normal to the graph at x = 5
m = -1 / f `(x)
f ` ( x ) = 
 m = - 3/34
m = - 3/34