Question 228552
Ok for this problem,

{{{(y^2-81)/(4y+36)}}}/{{{(y-9)/(18)}}}

You want to multiply the reciprocal of the second fraction to start solving:

{{{(y^2-81)/(4y+36)}}}x{{{(18)/(y-9)}}}

Now looking at the numerator of the first fraction, you can simplify by doing the foil method (backwards).  Here's how that would look:

{{{(y+9)(y-9)/(4y+36)}}}x{{{(18)/(y-9)}}}

Next, for the denominator on the first fraction, you can simplify 4y+36, by dividing a four out of it, here's how it would look:

{{{(y+9)(y-9)/(4)(y+9)}}}x{{{(18)/(y-9)}}}

Now, you can cross out the like terms from both fractions:

{{{1*cross((y+9))cross((y-9))/(4)cross((y+9))}}}x{{{(18)/1cross(y-9)}}}

Now, you're left with 

{{{18/4}}}

To simplify:  2 goes into both numbers easily

{{{9/2}}}