Answer:
The area of a red plate with radius 6cm is greater. 
Step-by-step explanation:
The general formula for the area of a circle is: 
A = πr², where 'r' represents the radius
To compare the areas of the plates, we can set up two different equations: 
Red plate:  A = π6² or 36π
Yellow plate: A = π3² or 9π
But, there are two yellow plates: 
9π + 9π = 18π
36π > 18π, so the area of the red plate is greater.