why sales tax of cash payments is excluded in the option

the following transactions took place during Alan’s first month of trading:
Credit sales of $121,000 exclusive of sales tax
Credit purchases of $157,110 inclusive of sales tax
Cash payments to credit suppliers of $82,710 inclusive of sales tax
All transactions are subject to sales tax at 20%.
What was the balance on Alan’s sales tax account at the end of his first month of trading?
A $1,985 DR
B $1,985 CR
C $15,770 DR
D $15,770 CR

answer is A

why cash payments to credit suppliers inclusive of sales tax excluded in the answer