Question

Salvador wrote 15 letters to friends each month for p months in a row. Write an expression to show how many total letters Salvador wrote

Answer 1

You said he wrote 15 letters to friends per month.

Let's call the the amount of months he wrote letters the variable "m"

You'd make that 15m (aka 15 * m since 15 per month)

Your math problem would be:
15m=x

Answer 2

Thank you.