Consider how rounding to a multiple of 16 (which is \(2^4\)) relates to the binary representation of the number in base -2. What happens to the least significant bits when rounding down?

Recall that in base -2, each digit represents a power of -2, and the place values alternate in sign. How can you isolate the part of the number that contributes to the lower 4 bits (i.e., the part that is less than 16 in magnitude)?

To round down to a multiple of 16, you need to "chop off" the lower 4 bits of the base -2 number. However, because the base is negative, simply truncating the lower bits may not work directly. Explore how to adjust the remaining higher bits to account for the removed lower bits, ensuring the result is correctly rounded down.