Question 971794
As per given proportionality conditions,
Let {{{A = k* t^2 * r^3}}} where k is any proportionality factor
When r=0.25, t=47
i.e {{{A = k* 47^2 * (0.25)^3}}}
=> {{{A/k = 47^2 * (0.25)^3}}}   -(i)
So, when t=345, we have,
{{{A/k = 345^2 * r^3}}}   -(ii)
From eqn. (i) and (ii),
{{{r^3 = 47^2 * (0.25)^3 / 345^2}}}   (Solve it)

And relatonship between t and r is given by initial condition

{{{t^2 * r^3 = 47^2 * (0.25)^3}}}