Sure, here are the sentences with the primary stress marked ('):

1. 'How 'many 'lessons do you 'have to'day? - I 'have 'four.
2. 'How 'many 'students does your 'class 'have? - It 'has thir'ty-six.
3. 'How 'many 'pencils do you 'have? - I 'have 'two.

In each sentence, the primary stress is typically placed on the key content words that carry the main meaning, such as "how," "many," "lessons," "have," "today," "four," "students," "class," "thirty-six," and "pencils."