Answer:
Length of rectangular strip = 12
area of rectangular strip =   2*12 = 24
Area of square =  x^2 = 12^2 = 144
Step-by-step explanation:
Area of square x^2
area of rectangle is given by length * width
Length of rectangular strip = x
width of rectangular strip = 2
area of rectangular strip =  length * width = 2*x = 2x
Area of square piece of paper when  rectangular strip is taken away from it 
= Area of square - area of rectangular strip 
= 
It is given that Area of square piece of paper when  rectangular strip is taken away from it is 120 square units.
Thus, 

Thus, 
either x+10 = 0 or x -12= 0
x = -10 or x = 12
but length cannot  be negative hence neglecting x = -10
hence value of x is 12.
Hence, 
Length of rectangular strip = 12
area of rectangular strip =   2*12 = 24
Area of square =  x^2 = 12^2 = 144