I was thinking the measurement for ;length should be 2.5n + 8 feet since width is 6n -2.5 feet , but you gave 2.5+ 8 feet, so i will solve it in both ways
Answer: Perimeter = 5 + 12n + 11 feet ; Perimeter = 17n+ 11 feet
Step-by-step explanation:
Using Length = 2.5+ 8 feet,
Perimeter of a rectangle is calculated as 2( l+ b)
Given that width=6n - 2.5 feet
length =2.5 + 8 feet
Perimeter =2( l+ b)= 2L + 2B
Perimeter= 2(2.5 + 8feet ) + 2( 6n - 2.5 feet)
Perimeter = 5 + 16feet + 12n - 5feet
Perimeter = 5 + 12n + 11 feet
Using Length = 2.5n+ 8 feet,
Perimeter of a rectangle is calculated as 2( l+ b)
Given that width=6n - 2.5 feet
length =2.5n+ 8 feet
Perimeter =2( l+ b)= 2L + 2B
Perimeter= 2(2.5n + 8feet ) + 2( 6n - 2.5 feet)
Perimeter = 5n + 16feet + 12n - 5feet
Perimeter = 5n + 12n + 11 feet
Perimeter = 17n+ 11 feet
simplified it would be - 
</h2><h2>Hope this helps!!</h2>