We have the next formula for the area of a rectangle
[tex]A=lw[/tex]
where l is the length and w is the width
in our case
l=6n+9
w=n
We substitute the expressions on the formula
[tex]A=(6n+9)n[/tex]
Then we simplify
[tex]A=6n^2+9n[/tex]
ANSWER
A=6n^2+9n
