I don't understand this question can someone help me with this please, please explain If u dont know try your best :D

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)

How long must $542 be invested at a rate of 7% to earn $303.52 in interest? in a easier way

If you have 12 feet of string and you cut it into equal length of 5 inches each how much string will be left