a. Since the volume is directly proportional to the cube of its radius, when you increase the radius by multiplying it by 2, then you increase the volume by multiplying it by 2^3, so your new volume is:

33.5 * 2^3 = 33.5 * 8 = 268 cm^3

To double check the answer, just plug in 4 for radius in the formula I gave you for the volume of the sphere, and you can see that the answer is correct

b. Similar to above, when the volume is multiplied by 2, that means that the radius is multiplied by cube root of 2, so your new radius is:

2 * cube root of 2

Again, to double check the answer, just plug in the radius in the formula for the volume of the sphere, and you can see that the answer is correct.

I hope this helped

Kia