Let's first define the states of matter. There are three states: solid, liquid, and gas. To differentiate between them we can take water as an example. In its solid state it would be ice, it has a definite shape. The liquid state would be the normal water that we drink, and it takes the shape of the container in which it is contained. The gaseous state would be the water vapor that is generated when we heat it, it has a larger volume and is dispersed in the environment.
Having clarified the states of matter, let us now define a mixture. A mixture is the combination of two or more substances. When the substances have the same state of matter and there is no difference between them is called homogeneous mixture, when you can differentiate one substance from another will be a heterogeneous substance.
To solve the question you can for example see the mixture of breakfast cereal with milk. We have two substances, milk in liquid state and cereal in solid state, we can differentiate between these two substances so we have a heterogeneous mixture.