All sides of squares are the same.
Area is found by doing length times width.
For squares, this can be represented as the square of the length of one side.
If you only know the area, then you must work backwards and do the inverse.
If you had to use squaring to get the area, then find the square root of the area to get the length of each side.
√1640 = 40.496913...
If you round this to the nearest tenth, this is about 40.5.
Since there is a 9 in the hundredths place, which is closer to +0.1 than +0.0, you round up to 40.5.
So rounded to the nearest tenth, the sides of the tabletop have a length of 40.5 inches.