Answer :
Since the parabola is given by [tex]8y=x^2[/tex], and [tex]x[/tex] is parameterized by [tex]x(t)=ct[/tex], it follows that when [tex]t=3[/tex] and [tex]x=4[/tex], we have
[tex]4=3c\implies c=\dfrac43[/tex]
So when [tex]t=2[/tex], the [tex]x[/tex]-coordinate of the point [tex]p[/tex] would be
[tex]x=\dfrac43(2)=\dfrac83[/tex]
I'm not sure how [tex]y[/tex] is parameterized, but my best guess is that you mean to say
[tex]y(t)=\dfrac{c^2}8t^2[/tex]
which means when [tex]t=2[/tex] we would get a [tex]y[/tex]-coordinate of
[tex]y=\dfrac{\left(\frac43\right)^2}82^2=\dfrac89[/tex]
[tex]4=3c\implies c=\dfrac43[/tex]
So when [tex]t=2[/tex], the [tex]x[/tex]-coordinate of the point [tex]p[/tex] would be
[tex]x=\dfrac43(2)=\dfrac83[/tex]
I'm not sure how [tex]y[/tex] is parameterized, but my best guess is that you mean to say
[tex]y(t)=\dfrac{c^2}8t^2[/tex]
which means when [tex]t=2[/tex] we would get a [tex]y[/tex]-coordinate of
[tex]y=\dfrac{\left(\frac43\right)^2}82^2=\dfrac89[/tex]