Your correct in saying 1 byte = 8 bit. However, 3072 Megabytes must first be converted to bits, so that then we can find the amount of Megabits. So, 3072 MB = 3072 megabyte = 3072*8 mb (megabit), is not true.
The correct working is:
3072 MB (Megabytes) * 1024 *1024 * 8 = 2.576980378x10^10 b...