What is the written form of the number 78?

i waited in the lobby of the post office until my number, 78, appeared on the screen.
a.
seventy-eight
b.
seventy eight

The written form of the number 78 should be option A. seventy-eight. Numbers are classified as compound words. It is a rule that when spelling out numbers, it should be connected with a hyphen. So the sentence should be, "I waited in the lobby of the post office until my number, seventy-eight, appeared on the screen."

C. c is the correct answer.