No, esa mochila es roja. La mía es azul. ¿De quién es la mochila roja? (No, that backpack is red. Mine is blue. Whose is the red backpack?)

Ejemplos:

"Just type 'Es de la profesora' and let’s go grab coffee," his friend Clara whispered, leaning over.

Whose backpack is that? – It’s mine. → _______________