how do I make this gradation?

[senjaez49486447]

I tried putting gradation on the images selected. However, the gradation splits into two objects.

I want it to be graded on combined objects instead. How do I do that?

[Ton Frederiks]

Try to select both and drag the Gradient Tool (G) across them.

[Monika Gause]

But you need to select them with the live paint selection tool as this is still a live paint group.

Read about live paint groups: How to create and work with Live Paint groups in Illustrator