Nathan earns a fixed pay of $250.25 a week for his normal 30 hours. For each additional hour he works, he receives $9.50.

Nathan's fixed pay is $250.25, so the amount he earns for his normal 30 hours is $250.25.

For each additional hour he works, he receives $9.50, so the amount he earns for x additional hours is 9.50x.
To find the total amount he earns, we add his fixed pay to the amount he earns for the additional hours: 9.50x + $250.25.
We want him to earn at least $312.00, so we can write the inequality 9.50x + $250.25 ≥ $312.00.