Remember that we can multiply or divide each side of any equality by the same non-zero number and get the equivalent equality. That simple rule creates even simpler one, the cross-multiplication rule.

If we have

*a*/

*b* =

*c*/

*d* we can

multiply each side by

*b* and get

*a* =

*b**c*/

*d*or divide each side by

*c* and get

*a*/(

*b**c*) = 1/

*d*So, basically, we can move any number from denominator of one side to the numerator of another or from numerator to the denominator.

Take a look at these animations to strengthen your understanding:

When we use cross-multiplication rule to solve this question we can easily find

*y*:

Then we can plug it in 9

*y*² and simplify to get the answer.