As you see, and it is almost obvious, this sequence is an arithmetic progression.

The first term is 12 and the common difference is -5.


On the number line, the distance between the first term and the last term is 

    12 + 203 = 215.


The number of gaps between the terms in the number line is   = 43.


Add 1 (one) to it, and you will get the number of terms of the progression: it is 43 + 1 = 44.    ANSWER


It is the simplest way to solve this and hundreds other similar problems.


Your intuition and your common sense will dictate you what to do . . . without memorizing any formulas.


CHECK.   To check, calculate the last term, using standard formula of an arithmetic progression


          =  = 12 - 43*5 = - 203.    ! Correct !