I believe the first question is 4 feet / 1 second and the second answer is 16 oz / 1 lb
I use an app called Socratic also it works very well!!
The formula for circumference is

.
To express the circumference exactly, plug the diameter in for

and put the

symbol in front of it. Don't multiply. This expresses the exact circumference.
Say you have the diameter of 17.
You can express the circumference with 17

.