Final answer:
Sunil owes Cara $500 and pays her $20 per day from his earnings. The equation representing his remaining debt D after x days is D = 500 - 20x.
Step-by-step explanation:
To determine the equation that represents Sunil's debt D after x days when he owes Cara $500 and makes $40 per day at his job, which he then gives half of his earnings to Cara until the debt is paid off, we can set up a linear equation. Each day he works, he earns $40, and he gives half of that, which is $20, to Cara. Thus, for each day Sunil works, his debt decreases by $20.
The equation representing Sunil's remaining debt D after x days would be:
D = 500 - 20x
This equation starts with the initial debt of $500 and subtracts $20 for each day that Sunil works and makes a payment.