There is about 30 g of Californium-252 left, how much time has elapsed?

You haven't provided two critical pieces of info needed to answer this question. First, what's the half-life of Californium-252, and second, what's the initial amount of Californium-252. Given these two values, you can then set up an exponential equation to find the time elapsed.

8 m/s because for him to get the same amount of energy as ray is putting out, bobby, who weighs half as much as ray, needs to run twice as fast.