1. The problem gives three numbers on cards: 3, 11, and 6. We are asked to find the number on Jeff's fourth card. 2. Without additional context, we assume a pattern or relationship exists among the numbers 3, 11, and 6 to predict the fourth number. 3. Check the difference between the numbers: 11 - 3 = 8 and 6 - 11 = -5. The differences are not consistent, so consider other patterns. 4. Consider if the fourth number could be related to the average, sum, or another arithmetic operation of the three given numbers. 5. Calculate the average: $\frac{3 + 11 + 6}{3} = \frac{20}{3} \approx 6.67$. 6. Since the problem lacks explicit instructions, a reasonable guess is the average rounded to the nearest integer, which is 7. 7. Therefore, Jeff's fourth card number is 7. Final answer: 7