Answer:
x = 2  is the correct answer :)
 
        
             
        
        
        
Put this into a scientific calculator 
1/3 x pi x 18 squared x 16
        
             
        
        
        
You can use the identity
  cos(x)² +sin(x)² = 1
to find sin(x) from cos(x) or vice versa.
  (1/4)² +sin(x)² = 1
  sin(x)² = 1 - 1/16
  sin(x) = ±(√15)/4
Then the tangent can be computed as the ratio of sine to cosine.
  tan(x) = sin(x)/cos(x) = (±(√15)/4)/(1/4)
  tan(x) = ±√15
There are two possible answers.
In the first quadrant:
  sin(x) = (√15)/4
  tan(x) = √15
In the fourth quadrant:
  sin(x) = -(√15)/4
  tan(x) = -√15
        
             
        
        
        
Answer:
In the elimination method you either add or subtract the equations to get an equation in one variable. When the coefficients of one variable are opposites you add the equations to eliminate a variable and when the coefficients of one variable are equal you subtract the equations to eliminate a variable.
Hope this helps!
If you need a more in-depth answer, don't hesitate to ask!