If the perimeter is 9 inches, each side is 3 inches.
The height of an equilateral triangle splits the triangle in two right sub-triangles: for example, consider a triangle ABC and the height AH starting from A, perpendicular to BC.
The triangle AHC is a right triangle, whose legs are AH and HC, and whose hypotenuse is AC.
AH is half the side, and AC is a side. So, we can use the Pythagorean theorem to find the height:

So, the area is

In a square, the sum of the length of 3 sides is 48.......a square has sides that are all equal.....so 48/3 = 16...so each side of the square is 16
in a rectangle, the difference between a length and a width is 7
if the width is the same as the side of the square...so the width of the rectangle is 16...so if the width = 16, and the difference between the length and the width is 7, then the length of the rectangle is :
W = 16
L - W = 7
L - 16 = 7
L = 7 + 16
L = 23 <==== the length of the rectangle
-4,-3,-2,-1,0
which means 4 numbers