Why does my function keep failing my JUnit test?

Why does my function keep failing my JUnit test?

This is one of my classes that I am testing. It keeps failing the
calculateVolume() method and I am not sure why.
package shape3D;
public class Sphere implements Cloneable {
private double myRadius;
private double myVolume;
private double mySurfaceArea;
private final static double pi = 3.14;
public static void main(String args[]){
Sphere sphere = new Sphere();
}
public double calculateVolume(){
myVolume = (4/3)*pi*(Math.pow(myRadius,3));
return myVolume;
}
public double calculateSurfaceArea(){
mySurfaceArea = ((4)*(pi)*(Math.pow(myRadius,2)));
return mySurfaceArea;
}
public double getSurfaceArea(){
return this.calculateSurfaceArea();
}
public double getVolume(){
return this.calculateVolume();
}
public void setRadius(double radius2){
myRadius = radius2;
}
public String toString(){
return "Volume: " + this.getVolume() + " Surface area " +
this.getSurfaceArea();
}
public Sphere clone (){
Sphere p = new Sphere();
p.setRadius(myRadius);
return p;
}
}
Here is the JUnit test case I am using
public class sphereTest {
@Test
public void testSphere(){
shape3D.Sphere sphere = new shape3D.Sphere();
sphere.setRadius(6);
assertTrue(sphere.calculateSurfaceArea()== 452.16);
assertTrue(sphere.calculateVolume()== 904.32);
The calculateSurfaceArea() stuff passes fine but the volume is failing and
I am not sure why.