budgeting

“Mr Grob started trading in 20X3, selling one product on credit. The following budgeted information for 20X4 has been gathered:

Credit sales:
Jan 20X4: $12,000
Feb 20X4: $15,000
Mar 20X4: $21,000

Receivables have recently been settling their debts 50% in the month following sale, and 50% two months after sale. A prompt payment discount of 3% is offered to those receivables paying in the following month.

The gross profit margin is expected to be 25%. Due to an anticipated continued increase in sales, Mr Grob intends to increase inventory levels in March 20X4 by $2,000, and it is intended that the payables balance is increased by $3,000 to ease cash flows in the same month.

Calculate the budgeted payment to suppliers in March 20X4.”

My answer:

21,000*0.75+2,000+3,000= 20,750

but what they did is that they subtracted 3,000 (21,000*0.75+2,000-3,000=14,750) and I don’t get it why… Can you explain why is that so?

For instance, If I want to increase accounts payable, doesn’t that mean I’ll add the accounts payable balance? If the payables are – 100 and I’ll add 100 payables, doesn’t that mean it becomes 200?

thanks in advance