Ok so I think I have this correct, but I'm not sure.

The question is: what is the frequency of green light, which has a wavelength of 4.90 x 10 ^-7 m?

Since all electromagnetic waves travel at
3.00 x 10^8 m/s (c), and
c= wavelength x frequency,

The problem is:
(3.00 x 10^8) / (4.90 x 10^-7) = frequency

Right?

I got .61 x 10^15 as a result.

Is this right?

2 answers

Yes, but I would put it in scientific notation 6.1 x 10^14 hz
In addition to putting it in scientific notation as Bob Pursley suggested, I would add another place. You have three significant figures in 4.90 and 3 s.f. in 3.00; therefore, you are allowed 3 in the answer or 6.12 x 10^14 Hz.