Question 7839
You can write the relationship between x and s & t as follows:

{{{x = k(s^2/t)}}} k is known as the constant of proportionality.

If you want to see the effect on x when s is doubled, just replace s with 2s.

{{{x = k((2s)^2)/t}}} = {{{k(4s^2)/t}}} = {{{4k(s^2)/t}}} which is 4 times the original equation for x.  So x is quadrupled when s is doubled.

Now let's double both s and t by substituting 2s and 2t into the original equation.

{{{x = k(2s)^2/2t}}} = {{{k(4s^2)/2t}}} = {{{k(2s^2/t)}}} = {{{2k(s^2)/t}}} and here, you can see that the effect on x is to double it when you double both s and t.