Step-by-step explanation: when you have a power to a power, like this example, it's essentially saying, y to the power of 4 times y to the power of four times times y to the power of 4 times y to the power of 4 times y to the power of 4, so y to the fourth is being repeated 5 times, so just multiply 5*4 to get 20.
The ratio of areas is the square of the ratio of perimeters (or any linear measure). Then the ratio of perimeters is the square root of the ratio of areas: .. √(16/49) = 4/7