There's a mouse and three doors:

The first door takes the mouse to a cheese in 3 minutes.

The second door takes the mouse to the initial state (he has to choose a door again) in 5 minutes.

The third door takes the mouse to the initial state in 5 minutes.

Always the mouse chooses a door randomly and independient.

What's the expected value of the time the mouse takes to get the cheese?

i would really apreacciate a help here