Question

How do I do number 1 and 2? I've tried them several times, but I still can't get it.

Answer 1

For question 1, you need to look at the number and decide on the closest square numbers.
For this example, the two closest square numbers to 160 are 144 (12²) and 169 (13²). 
Therefore, we can say that the square root of 160 must be between 12 and 13.

For question 2, when we find the area of a 4-sided shape, we have to multiply the 2 adjacent sides. In this case, as the shape is a square when we multiply the 2 sides it is this same as squaring 1 side. This means that when we find the side from an area of a square you take the square root.
We found in question 1 that 13² is 169, therefore the square root is 13 and the sides must each be 13 ft long.