In order to solve this problem, you need to know how to solve for the area of squares. After that, it's just one-step algebra and, as you note, rounding.
The area of any parallelogram (including a square) is the length of its base side times the length of its height side. For squares, the base and the height are always the same: that's what makes it a square!
1) Let s = length of one side
3) s = √50
4) Can you use your calculator to find the square root of 50? If calculators aren't allowed, do you know any perfect squares (whole numbers multiplied by themselves) that are close to 50?
I bet you can figure it out from here....