This is related to derivatives.

`y = x^5 ` ----(1)

Let us say for for marginal change in `deltax` the change in y is `deltay `

`y+deltay = (x+deltax)^5` ----(2)

(2)-(1)

`deltay = (x+deltax)^5-x^5`

Rate of change means `deltay/(deltax)`

`(deltay)/deltax = [(x+deltax)^5-x^5]/(deltax)`

When `(deltay)/(deltax) ` be a small marginal change;

`lim_(xrarr0)(deltay)/deltax = lim_(xrarr0)[(x+deltax)^5-x^5]/(deltax)`

`lim_(xrarr0)(deltay)/(deltax)` referred as the derivative of a function.

Therefore rate of marginal change can be expressed as the derivative.

`(dy)/dx = 5x^4`

Rate of change at x = 2 and y = 32;

`((dy)/dx)_(x=2) = 5*2^4 = 80`

So the statement is correct and we should agree with that.