Hello!
The answer is:
The simplified expression is:
![(x + y + 3)(x + y - 4)=x^(2) +y^(2) +2xy-x-y-12](https://img.qammunity.org/2020/formulas/mathematics/middle-school/w5fjj78j9sbqynjhyx92i23104g26pmvu6.png)
Why?
To solve the problem, we need to remember how to use the distributive property and how to add like terms.
The distributive property can be defined as follow:
![(a+b)(c+d)=ab+ad+bc+bd](https://img.qammunity.org/2020/formulas/mathematics/middle-school/j4yzdh9n9p9fqb45xd155t1vkcnd7nyf02.png)
The like terms are the terms that share the same variable and the same exponent, for example:
![3x+x+ x^(2)=x^(2) +4x](https://img.qammunity.org/2020/formulas/mathematics/middle-school/3x0goq9jucvq3gusrvotc9dylsxb67ry58.png)
We were able to add the first and the second term because they share the same variable and the same exponent.
Now, we are given the expression:
![(x+y+3)(x+y-4)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/zqs2h6munomw88f6hmiatksn6s9e5vftzd.png)
So, simplifying we have:
![(x + y + 3)(x + y - 4)=(x*x)+(x*y)-(4*x)+(y*x)+(y*y)-(4*y)+(3*x)+(3*y)-(3*4)\\\\(x + y + 3)(x + y - 4)=x^(2) +xy-4x+xy+y^(2)-4y+3x+3y-12\\\\(x + y + 3)(x + y - 4)=x^(2) +y^(2) +2xy-x-y-12](https://img.qammunity.org/2020/formulas/mathematics/middle-school/1u41j1057in8gx6coxzrr8yuxtik8g4plw.png)
Hence, we have that the simplified expression is:
![(x + y + 3)(x + y - 4)=x^(2) +y^(2) +2xy-x-y-12](https://img.qammunity.org/2020/formulas/mathematics/middle-school/w5fjj78j9sbqynjhyx92i23104g26pmvu6.png)
Have a nice day!