QUES: Only then am I able to help them

correct the punctuation.

CORRECTED: Only then am I able to help them."

QUES: He also learnt mathematics from the books of Clavius

correct the punctuation.

CORRECTED: He also learnt mathematics from the books of Clavius .

QUES: A total of 352 researchers responded

correct the punctuation.

CORRECTED:
A total of 352 researchers responded.