What is the first thing an informal letter writer should write, and how does an informal letter differ from a formal letter?

The question asks for the first thing an informal letter writer should write.
"Ohun akoko ti alaroko onileta aigbagbefe gbodo ko ni (a) deeti (b) ila-pa-oro (d) akele"
Translation: "The first thing an informal letter writer should write is (a) date (b) salutation (d) address."
In informal letter writing, the sender's address is written first. 'Akele' means address.

The correct answer is (d) akele.

The question asks how an informal letter differs from a formal letter.
"Leta aigbagbefe yato si