Shape of the Garden:
The shape of the garden is described as rectangular in the middle and semi-circular at the ends. This means that the garden consists of a rectangular portion in the center and two semi-circular portions at each end.

Length of the Rectangle:
The length of the rectangle is given as 20 - (3.5 + 3.5) meters. This means that the length of the rectangle is obtained by subtracting the combined lengths of the two semi-circular portions from 20 meters.

Calculating the Length of the Rectangle:
To calculate the length of the rectangle, we need to subtract the total length of the semi-circular portions from the total length of the garden.

Total Length of the Garden = 20 meters
Length of Each Semi-circular Portion = 3.5 meters + 3.5 meters = 7 meters
Length of the Rectangle = Total Length of the Garden - Length of Each Semi-circular Portion
= 20 meters - 7 meters
= 13 meters

Therefore, the length of the rectangle is 13 meters.

Calculating the Area:
To calculate the area of the garden, we need to find the area of the rectangular portion and the area of the two semi-circular portions separately, and then add them together.

Area of the Rectangle = Length of the Rectangle * Width of the Rectangle
= 13 meters * Width of the Rectangle

To determine the width of the rectangle, more information or measurements are needed. Without the width, we cannot calculate the area of the rectangle.

Area of the Semi-Circular Portions = (1/2) * π * (Radius of the Semi-circle)^2
= (1/2) * π * (3.5 meters)^2
= (1/2) * 3.14 * (3.5 meters)^2

To calculate the area of the garden, we need to add the area of the rectangle and the area of the semi-circular portions.

Area of the Garden = Area of the Rectangle + 2 * Area of the Semi-Circular Portions

Calculating the Perimeter:
To calculate the perimeter of the garden, we need to find the sum of the lengths of all the sides of the garden.

Perimeter of the Garden = Length of the Rectangle + 2 * Length of the Semi-Circular Portions

The length of the semi-circular portions is equal to the circumference of a circle with a radius of 3.5 meters.

Length of the Semi-Circular Portions = 2 * π * Radius of the Semi-Circle
= 2 * π * 3.5 meters

To calculate the perimeter of the garden, we need to add the length of the rectangle and the length of the semi-circular portions.

Perimeter of the Garden = Length of the Rectangle + Length of the Semi-Circular Portions + Length of the Semi-Circular Portions

In summary, to find the area and perimeter of the garden, we need more information such as the width of the rectangle. With that information, we can calculate the area of the garden by adding the area of the rectangle and the area of the semi-circular portions, and the perimeter of the garden by adding the length of the rectangle and the length of the semi-circular portions.