Answer
$$(9 + 10y)(9 - 10y)$$
Work Step by Step
To factor the difference of two squares, we use the formula:
$$A^2 - B^2 = (A + B)(A - B)$$
For this binomial, we take the square root of the leading coefficient $(81)$ to get $A = 9$ and the square root of the constant $(100)$ to get $B = 10$.
So we now plug these two values into the formula for factoring the binomial:
$$(9 + 10y)(9 - 10y)$$
