Hey there :)
( x + y + 3 )( x + y - 4 )
Distribute each factor
x ( x ) +x ( y ) + x ( - 4 ) + y ( x ) + y ( y ) + y ( - 4 ) + 3 ( x ) + 3 ( y ) + 3 ( - 4 )
x² + xy - 4x + yx + y² - 4y + 3x + 3y - 12
Combine, if any, the like terms
x² - 4x + 3x + xy + yx + y² - 4y + 3y - 12
x² + - x + 2xy + y² - y - 12