Robert was reviewing the water bill for his carwash business and determined that the highest bill, $7,000, occurred in July when 4,000 cars were washed and the lowest bill, $4,000, occurred in February when 1,000 cars were washed. What was the fixed portion of the water bill? (Round intermediary calculations to the nearest cent. Use the "high" data month to calculate your final answer. Do not use the "low" month, as it will result in an approximation of the cost.) OA. $4,000 B. $3,000 OC. $6,000 OD. $1,000