Williams Inc. produces fluorescent lightbulbs for commercial use. The accounting manager is attempting to estimate the total cost for the next quarter using the high-low method. He has compiled data and found the high and low costs are $10,000 and $6,000, respectively, and the associated cost drivers are 7,000 and 3,000 packs, respectively. What is the value for b (the variable cost per unit)? What is the value for a (the fixed quantity)?