To expand the expression (3a - xy)(3a + xy), we can use the formula for multiplying two binomials: (a + b)(a - b) = a2 - b2 If we let a = 3a and b = xy, then we have: (3a - xy)(3a + xy) = (3a)2 - (xy)2 Expanding the terms on the right side, we get: (3a)2 - (xy)2 = 9a2 - x2y2 Therefore, the answer is 9a2 - x2y2.