I don't understand this question and how they solve it?

5.5.2 Example: change in production costs Close Brickett Co makes a product which has a variable production cost of $8 and a variable sales cost of $2 per unit. Fixed costs are $40,000 per annum, the sales price per unit is $18, and the current volume of output and sales is 6,000 units. The company is considering whether to have an improved machine for production. Annual hire costs would be $10,000 and it is expected that the variable cost of production would fall to $6 per unit. Required (a) Determine the number of units that must be produced and sold to achieve the same profit as is currently earned, if the machine is hired. (b) Calculate the annual profit with the machine if output and sales remain at 6,000 units per annum.Solution The current unit contribution is $(18 - (8+2)) = $8 (a) $ Current contribution (6,000 x $8) 48.000 Less current fixed costs 40,000 Current profit 8.000 With the new machine fixed costs will go up by $10,000 to $50,000 per annum. The variable cost per unit will fall to $(6 + 2) = $8, and the contribution per unit will be $10. $ Required profit (as currently earned) 8,000 Fixed costs 50,000 Required contribution 58.000 Contribution per unit = $10 Sales required to earn $8,000 profit = 5,800 units (b) If sales are 6,000 units $ Sales (6,000 x $18) 108,000 Variable costs: production (6,000 x $6) 36,000 sales (6,000 x $2) 12,000 48,000 Contribution (6,000 x $10) 60,000 Less fixed costs 50,000 Profit 10,000 Alternative calculation $ Profit at 5,800 units of sale (see (a)) 8,000 Contribution from sale of extra 200 units (x $10) 2,000 Profit at 6,000 units of sale 10,000