And I need to find the Thevenins equivalent circuit. When I first got the problem I confidently threw some voltage divider equations around and got the thevenin voltage as 0.75V. But that's wrong. It's actually 0.5V. Why? Thats where I need help! If you could explain that to me I would be very thankful. Anyways, the next was the equivalent resistance, which I found by using parallel resistance formulae to be 50Ω. Wrong again, it's 67Ω. I've had difficulty with this problem before, and last time after an arduous time I finally solved it the right way, but I can't find those notes at the moment.

If someone could please at least tell me what I did wrong I would be immensely thankful.