Question

All the three of them used to sit and discuss the community's problem - pick out modal auxiliary and state function

Answer 1

used to,shows confirmation

Answer 2

Answer is “ used to “, which is an modal auxiliary verb.

The nature of helping verbs or auxiliary verbs are given by will, shall, may, might, can, could, must, ought to, should, would, used to, need are used in conjugate with principal verbs to express shades of moodiness and time.

The combination of assisting verbs with main verbs creates what is termed as verb phrases or verb strings.

In the given sentence, " All the three of them used to sit and discuss the community's problem " the words  “used to “ are helping or auxiliary verbs.