What is the range of f (x) = 4•0.5^x?

The range is the output, which would be the Y value.

The Y value would be calculated based on the input value for x.

any positive number raised to any value of x would be a positive number so 0.5^x would always be positive.

That would be multiplied by 4, which is a positive value, so the output (Y value) would always be positive.

The range for this would be (0,∞)