Each week Ingrid earns a fixed salary and a sales commission that is a fixed percentage of her sales for that week. Ingrid has no other sources of income. Last week Ingrid's total earnings were $500 and her sales were $2,000. This week Ingrid's total earnings were $700 and her sales were $6,000. What is the percentage rate for Ingrid's sales commissions?

This option suggests an extremely low commission rate which would not account for Ingrid's total earnings given her sales figures. With sales of $2,000 and a commission of only 0.05%, her total earnings would not reach $500, indicating that this option is incorrect.

If Ingrid's commission rate were 4%, her commission from sales of $2,000 would yield only $80, resulting in total earnings of far less than $500 when combined with her fixed salary. Similarly, with sales of $6,000, the earnings would not reach $700, making this option invalid.

A commission rate of 20% would result in excessive earnings based on her sales figures. For instance, at 20%, her commission for $2,000 in sales would be $400, leading to total earnings of $800, which exceeds the reported $500.

This option suggests an even higher commission rate, which would lead to total earnings that far surpass what Ingrid reported. At 30%, her commission for $2,000 in sales would be $600, resulting in total earnings of $1,000, which is not possible according to the question.