You just substitute the value of x in the given equation:
f(x) = 2x^2 - 5
f(-4) = 2 (-4)^2 -5 = 27
f(x) : a name given to the equation
f(-4): refer to the equation when the value of the independent variable x has the value between the brackets. 
        
             
        
        
        
Answer: The answer is y=-3x
Step-by-step explanation: You can see in the picture that the line is going down which represents a negative slope so you can eliminate C and D. Now you are left with A and B. 1 unit up is equal to 3 so the rise over run is -3/1 and that translates to Y=-3x answer B 
 
        
             
        
        
        
Do you know the multiples of 10
        
             
        
        
        
Amplitude: 1/4 (= |a|)
Frequency: 1/2 (= |b|)
Period: 4pi (= 2pi/|b|)