If increasing physical capital increases productivity, why would a company not buy newer, faster computers for all its workers every year?

Kubin company’s relevant range of production is 18,000 to 22,000 units. when it produces and sells 20,000 units, its average costs per unit are as follows: average cost per unit direct materials $ 7.00 direct labor $ 4.00 variable manufacturing overhead $ 1.50 fixed manufacturing overhead $ 5.00 fixed selling expense $ 3.50 fixed administrative expense $ 2.50 sales commissions $ 1.00 variable administrative expense $ 0.50 required: 1. for financial accounting purposes, what is the total amount of product costs incurred to make 20,000 units? 2. for financial accounting purposes, what is the total amount of period costs incurred to sell 20,000 units? 3. for financial accounting purposes, what is the total amount of product costs incurred to make 22,000 units? 4. for financial accounting purposes, what is the total amount of period costs incurred to sell 18,000 units?