It’s something from khan academy

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)

Ineed me i stuck and i don’t want to get it wrong

Cd is the perpendicular bisector of both xy and st, and cy=20. find xy.