Why Kilo means thousand and mega means million, so 1 MHz = 1000 kHz. To convert kilohertz to megahertz you divide by 1000, which moves the decimal point three places left: 28400 / 1000 = 28.400 MHz. That lands in the 10 meter band, a familiar HF frequency.
Watch out The choice reading 2.800 MHz shifts the decimal four places instead of three, and 284.00 MHz multiplies instead of divides; kHz to MHz always makes the number smaller.
kHz to MHz: slide the decimal 3 places LEFT. 28400 kHz becomes 28.400 MHz.