Geometric/ Sigma Problems

Okay so I'm having trouble with these questions.

1. If ...

∞

Σ (sinx)^ k-1 =6 determine x to the nearest degree. (0° ≤ x ≤ 90°

k=1

2. Suppose that you drop a ball from a window 50 meters above the ground. The ball bounces to 50% of its previous height with each bounce. If the ball continues to bounce in this manner, how far will it have traveled, up and down, from the time it was dropped from the window?

3. Solve for x:

8

Σ (ix-3) =76

i=4

4. A new $12,000 automobile decreases in value by 25% each year. What will be its value 7 years from now?

I've tried everything and i'm still getting the wrong answer.

Thanks in advance! <3