Which is the initial value that shrinks an exponential growth function by 50%?

1/5
1/4
1/3
1/2

Suppose that the exponential growth function is  y = 4^x.

If x = 1, then y = 4^1 = 4.
If x = 3, then y = 4^3 = 64.

Let the initial value be 1/2.

The growth function is now y = 1/2 * 4^x.

If x =1, then y = 2 which is half of the y value before adding the 1/2.

If x = 3, then y = 1/2 * 64 = 32.

1/2

Ya i could just need to know what type of math