Please answer correctly

Simplify (a/b - b/a) times (a - a^2/a+b) a - a^2/a=b is a mixed number

Me because some of question i don’t understand

If the speed of an electromagnetic wave is 100,000 cm/s and its wavelength is 100 cm, what is its frequency? a) 100,000 cycles per second (hz) b) 1 × 10-3 cycles per second (hz) c) 10,000,000 cycles per second (hz) d) 1,000 cycles per second (hz)