Difference of two squares will be 
16y^2 -x^2 = (4y -x)(4y +x)
so the second choice 
        
                    
             
        
        
        
$750 / $30 = 25 maths teaching kids
$350 / $25 = 14 maths starter kits
if you wanted to see if it was right, you would just do 14*25 and you would get $350
hope I helped!!
        
             
        
        
        

It's clear that for x not equal to 4 this function is continuous. So the only question is what happens at 4.
<span>A function, f, is continuous at x = 4 if 
</span><span>

</span><span>In notation we write respectively
</span>

Now the second of these is easy, because for x > 4, f(x) = cx + 20. Hence limit as x --> 4+ (i.e., from above, from the right) of f(x) is just <span>4c + 20.
</span>
On the other hand, for x < 4, f(x) = x^2 - c^2. Hence 

Thus these two limits, the one from above and below are equal if and only if
 4c + 20 = 16 - c²<span> 
 Or in other words, the limit as x --> 4 of f(x) exists if and only if
 4c + 20 = 16 - c</span>²

That is to say, if c = -2, f(x) is continuous at x = 4. 
Because f is continuous for all over values of x, it now follows that f is continuous for all real nubmers 