1 foot is 12 inches. So just divide 81 by 12.
81/12 = 6.75
So your answer is 6.75 feet.
When writing the equation keep in mind that 7 + x is said as a term that is squared so it has to be squared while it's still together; (7 + x)².
Square root of 12 (

)
Square root of 18 (

)
You can multiply these two together to get:

Therefore your answer is 6 square root of 6.
Use m-a-t-h-w-a-y they are awesome. Or m-y-m-a-t-h-l-a-b