If the ratio of length and breadth of a rectangle is $\text{3}:\text{2}$ and its perimeter is $\text{4}0$ , then length of rectangle is

1. Let the length of the rectangle be 3x and the breadth of rectangle be 2x, as given in the ratio 3:2.
2. The formula for the perimeter of a rectangle is: 
   Perimeter = 2 × (Length + Breadth)
3. Substitute the values into the formula: 
   2 × (3x + 2x) = 40
4. Simplify the equation: 
   2 × 5x = 40
5. Divide both sides by 2: 
   10x = 40
6. Divide by 10 to find the value of x: 
   x = 40 ÷ 10 = 4
7. Now, calculate the length of the rectangle: 
   Length = 3x = 3 × 4 = 12 units
8. We also verify the breadth of rectangle: 
   Breadth = 2x = 2 × 4 = 8 units

Final Answer:

The length of the rectangle is 12 units, and the breadth of rectangle is 8 units.