Given : ABCF is a Rectangle
⇒ AB = CF
Given : AB = 6 cm
⇒ CF = 6 cm
Perimeter of a Rectangle is given by : 2(Length + Width)
Given : Perimeter of the Rectangle = 20 cm
⇒ 2(6 + BC) = 20
⇒ 6 + BC = 10
⇒ BC = 4
Given : BD = 9
But, We can See that : BD = BC + CD
⇒ CD + 4 = 9
⇒ CD = 5
We know that :
✿ 
Where : a and b are Lengths of Parallel Sides and Height is Length between those Parallel Sides
In the Given Trapezium :
The Parallel Sides are CD and EF and Height is CF
Given : EF = 3 cm


Answer:
y = (3 × 10^8 m/s)/x
Step-by-step explanation:
Speed of a wave is given by the product of wavelength and frequency.
Thus; speed = frequency × wavelength
If x = wavelength and y = frequency then speed will be;
speed = yx
Thus to get wavelength, y;
y = speed/x , but speed is 3 × 10^8 m/s
Thus;
y = (3 × 10^8 m/s)/x