Sales in December = 10,000*15.90 = $159,000
For 5% forecast growth each month;
Sales in January = (1+0.05)*Sales in December = 1.05*159,000 = $166,950
Sales in February = (1+0.05)*Sales in January = 1.05*166,950 = $175,297.50
The company should budget for $175,297.50 sales in February.