Question 1054164
Multiply numerator and denominator by {{{(y+9)(y-9)}}},
{{{(y/(y+9)-y/(y-9))/(y/(y+9)+y/(y-9))=(y(y-9)-y(y+9))/(y(y-9)+y(y+9))}}}

 {{{(y/(y+9)-y/(y-9))/(y/(y+9)+y/(y-9))=((y^2-9y)-(y^2+9y))/((y^2-9)+(y^2+9))}}}
{{{(y/(y+9)-y/(y-9))/(y/(y+9)+y/(y-9))=(-18y)/(2y^2)}}}
{{{(y/(y+9)-y/(y-9))/(y/(y+9)+y/(y-9))=-9/y}}}