Answer: 4 People were at the dinner.
Equation: 2x + 4 = 12
Step-by-step explanation: We know that there are 4 pieces left. So we can just take away 4 from 12. When that's done, we're left with 8 eaten slices. Then divide the 8 slices by the number of pieces per person. Therefore, 8/2 gives us 4.
I took algebra last year and loved it! I hope this helps!