Awave is traveling down a string at 21 m/s. (a) what is the wave's amplitude? (b) what is the wave's wavelength? (c) what is the wave's frequency? (d) what is the wave's period?

From the given information, the only thing we can tell is the wave's speed ... 21 m/s .
That also happens to be the product of it's (frequency) x (wavelength), but we can't say what either one alone is.

None of the items listed can be calculated without more information.

small = small current large mag large current

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.