You cannot - without additional information.
measure it
You need to know the length and width of the desk before you can determine the area. Multiply the length by the width to get your answer (length x width = area).
length x width
If volume can be provided then by using width, and height length can be found
multiply the width by 2 and then subtract that to the perimeter then divide the answer by 2 to get the length
The perimeter is equal to length + length + width + width while area is length x width. Both measurements are found by using width and length.
measure them.
Square root the area. The length and width of a square are always the same and length times width is the area so this is how you get the area.
First, determine the width (in). The width (in) is calculated to be : 6. Next, determine the length (in). The length (in) is measured to be: 12. Next, determine the millage. The millage is found to be: 3. Finally, calculate the Poly Bag Weight using the formula above:
height*length*width = volume Divide both sides by length*width to find the height: height = volume divided by length*width
Area = 0.5*(5+7)*3 = 18 square units
Given what? Probably measure it