Final answer:
To find out for what amount of sales Plan A is better than Plan B, we use the inequality 2500 + 0.06x > 3000 + 0.04x. This represents when the earnings from Plan A exceed the earnings from Plan B.
Step-by-step explanation:
To determine for what amount of monthly sales Plan A is better than Plan B, we need to set up an inequality comparing the total earnings one would get using each plan based on sales. For Plan A, which offers a salary of $2,500 per month plus a 6% commission on sales, the earnings can be represented as 2500 + 0.06x, where x represents the amount of monthly sales. For Plan B, with a salary of $3,000 per month plus a 4% commission on sales, the earnings are represented as 3000 + 0.04x. To find out when Plan A is better, we set Plan A's earnings greater than Plan B's earnings:
2500 + 0.06x > 3000 + 0.04x
This inequality shows the conditions under which Plan A provides more income than Plan B based on the sales x. Therefore, the correct answer is a) 2500 + 0.06x > 3000 + 0.04x.