Final answer:
Theresa will now be spending 0.3% of her salary on auto insurance.
Step-by-step explanation:
To find the percent of Theresa's salary that will now be spent on auto insurance, we need to calculate the increase in insurance cost as a percentage of her salary. Since her insurance is increasing from $65 to $68 per month, the increase is $68 - $65 = $3 per month. Let's assume Theresa earns a monthly salary of $1000. So, the percentage increase in her auto insurance cost is (3/1000) * 100 = 0.3% of her salary.