It would be 8x² - 15y² + xy
(4x + 5y) (2x - 3y) + 3xy
multiplying the terms in brackets
(4x) (2x - 3y) + (5y) (2x - 3y) + 3 xy
multiplying with each terms inside the bracket
(4x)(2x) - (4x) (3y) + (5y) (2x) - (5y) (3y) + 3xy
doing the product each of the pair of terms
8x² - 12xy + 10xy - 15y² + 3xy
taking the sum of terms with coefficient "xy"
8x² - 15y² -2xy + 3xy
8x² - 15y² + xy