Question 1056248
y varies inversely with x.
<pre>
{{{y}}}{{{""=""}}}{{{k/x}}}
</pre>
If y = 14 when x = 12, 
<pre>
Substitute that in

{{{14}}}{{{""=""}}}{{{k/12}}}

Solve for k

Multiply both sides by 12

{{{168}}}{{{""=""}}}{{{k}}}

Substitute that in 

{{{y}}}{{{""=""}}}{{{k/x}}}

{{{y}}}{{{""=""}}}{{{168/x}}}  <-- that's the formula
</pre>
find x when y is 21.
<pre>
Substitute 21 for y

{{{y}}}{{{""=""}}}{{{168/x}}}

{{{21}}}{{{""=""}}}{{{168/x}}}

Multiply both sides by x

{{{21x}}}{{{""=""}}}{{{168}}}

Divide both sides by 21

{{{x}}}{{{""=""}}}{{{8}}}

Edwin</pre>