It's either the area of a cylinder or volume of a cylinder. You can find both at math.com.
C. 480
Explanation: I’m pretty sure you’re looking for the perimeter. Therefore, since you have a rectangle, you’ll have 4 sides. The measures are 100 by 140 so you’ll put 100 and 140 on the other sides and simply add them up.
Given
we have
Squaring both sides, we have
And finally
Note that, when we square both sides, we have to assume that
because we're assuming that this fraction equals a square root, which is positive.
So, if that fraction is positive you'll actually have roots: choose
and you'll have
Which is a valid solution. If, instead, the fraction is negative, you'll have extraneous roots: choose
and you'll have
Squaring both sides (and here's the mistake!!) you'd have
which is not a solution for the equation, if we plug it in we have
Which is clearly false