Help: Inheritance 3. Mendel's rule?

Hello, I need help with this task, please. I don't understand it at all. Thank you very much 🙂

Two wood snails that are homozygous for shell characteristics are crossed. One parent has a red, banded shell, the other a yellow, unbanded one. All offspring have a red, unbanded shell. State the mode of inheritance.

Create a crossbreeding scheme from the parental generation to the second filial generation and explain the results. Choose alphabetical letters.