You receive a TELEX with the senders I.D. of 336640927. What type of terminal sent this message to your vessel?

Correct Answer: Option C — Inmarsat-B

Inmarsat-B mobile earth stations utilize a 9-digit identification format beginning with the digit 3. A sender ID starting with 3 indicates an Inmarsat-B terminal transmitting over the satellite network rather than an Inmarsat-C unit.