The point on the curve $y^2=8 x$ for which the abscissa and ordinate change at the same rate is :

(2, 4)

$y^2=8 x$     .......(1)

differentiating a function on both sides w.r.t to a variable t

$\frac{d}{d t}\left(y^2\right)=\frac{d}{d t}(8 x)$

$= 2 y \frac{d y}{d t}=8 \frac{d x}{d t}$       .......(2)

for all rate of change of x and y

let $\frac{d y}{d t}=\frac{d x}{d t}=k$

So eq. (2) is

2yk = 8k

⇒  2y = 8 ⇒ y = 4

from (1) extracting value of x

so (4)² = 8x

x = 16/8

x = 2

So (x, y) = (2, 4) →  same rate of charge of both variables