To find the total amount Samuel spent at the market on both days, we can break down his purchases each day:
Day 1:
- Apples: 3 pounds at \(x\) dollars per pound = \(3x\) dollars
- Spinach: 2 bags at \(y\) dollars each = \(2y\) dollars
Total spent on Day 1: \[ 3x + 2y \]
Day 2:
- Apples: 5 pounds at \(x\) dollars per pound = \(5x\) dollars
- Spinach: 3 bags at \(y\) dollars each = \(3y\) dollars
Total spent on Day 2: \[ 5x + 3y \]
Now, we combine the total from both days: \[ (3x + 2y) + (5x + 3y) = 3x + 5x + 2y + 3y = 8x + 5y \]
Therefore, the expression that represents the total amount he spent at the market on both days is: \[ \boxed{8x + 5y} \]