Question 73404
<pre>

    3x + y = 6
     x - y = 1
                     </pre>
Add the 2 equations. Add 3x to x, y to -y, and 6 to 1
<pre>

    4x     = 7
    
                     </pre>
Now solve for x

{{{4x=7}}}
{{{x=7/4}}}
Plug this into {{{x-y=1}}}
{{{(7/4)-y=1}}}
{{{-y=1-(7/4)}}}
{{{-y=(4-7)/4}}}
{{{-y=-3/4}}}
{{{y=3/4}}}
Check:
<pre>

    3(7/4) + 3/4 = 6
      7/4 - 3/4 = 1
                     </pre>

<pre>

    21/4 + 3/4 = 6
      4/4 = 1
                     </pre>

<pre>

    24/4 = 6
      1=1 Works
                     </pre>

<pre>

      6 = 6 Works
      1 = 1 Works
                     </pre>
<p>

Since x varies directly as y^2, the equation looks like
{{{y^2=kx}}}
So just plug in x=20 and y=2 to find k
{{{2^2=k*20}}}
{{{4/20=k}}}
{{{k=1/5}}}
Now plug k into the equation to find x when y=10
{{{y^2=(1/5)x}}}
{{{10^2=(1/5)x}}}Plug in y=10
{{{5*10^2=x}}}
{{{x=500}}}