Y=x3, vertically stretch by a factor of 4. how would the final equation look like?

The function is 

a vertical stretch means that if (a, b) is in the original function, the second function will contain the point:

(a, 4b)

For example: (2, 8) is in the graph of the original function.

If the graph of the function is stretched vertically by a factor of 4, this means that (2, 8)  becomes (2, 8*4)=(2, 32)

So to describe this stretch, the equation must be