This is the volume of the sphere & is not at all a linear function.
A linear function of the form of y=kx (k is a given number/coefficient) where
y & x grow at the same rate. Then whatever the input (x) it will generate an output (y) always in the ration y/x, whereas v=4/3 πr³ (coefficient =k =4/3(π), if r increase by 2 units v will increase by 2³ =8 & for r = 3, v increase by 3³ =27.
In short v increases quicker than r. No it's not a linear function
