Call the sides of the square X. The perimeter is the sum of the sides, or 4X.
The rectangle's length is x+14 and width is x+10 (x extended the given lengths.) Its perimeter is 2L + 2W = 2(x+14) + 2(x+10) = 2x+28+2x+20 = 4x + 48.
The rectangle's perimeter (4x+48) is at least (meaning greater than or equal to) twice the perimeter of the square (2*4x).
4x+48 >= 8x Solve for x....subtract 4x from both sides.
48 >= 4x Divide both sides by 4: 12>=x.
x can be 12 or less.