Answer:
![x^2+15x+36](https://img.qammunity.org/2021/formulas/mathematics/middle-school/xmmxdcg2305g34e3u4sird2lcx1r4ztti9.png)
Explanation:
The complete question is shown in the attachment.
The length of the rectangle is x + 12. The width of the rectangle is x + 3.
Recall that area of a rectangle is
![Length * Width](https://img.qammunity.org/2021/formulas/mathematics/middle-school/5jrnhqab4h6f0tmvchxp76wackfmx6ra6u.png)
In terms of x, the area is
![(x+12)(x+3)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/p5ts7iblmq5en40gihw79jscwxv170y1w0.png)
Recall the distributive property of real numbers:
![(a+b)(c+d)=a(c+d)+b(c+d)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/o1lpe2bbonq1qhttndb4fzsp8rcp1kub0c.png)
We apply this property to get:
![(x+12)(x+3)=x(x+3)+12(x+3)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/6efvgsxxvvw48mogvyyasxve54tg4agx8k.png)
We expand again to get:
![(x+12)(x+3)=x^2+3x+12x+36](https://img.qammunity.org/2021/formulas/mathematics/middle-school/63r49c8z65vh6bblnu4w5jj1zz5y2xrpwg.png)
We now simplify to obtain:
![(x+12)(x+3)=x^2+15x+36](https://img.qammunity.org/2021/formulas/mathematics/middle-school/ed9k6mtu2vx3tzaad5igtz6vdvnqjrity2.png)
The area of the rectangle is
![x^2+15x+36](https://img.qammunity.org/2021/formulas/mathematics/middle-school/xmmxdcg2305g34e3u4sird2lcx1r4ztti9.png)