Answer: It equals y to the twentieth power.
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.