Help please I really need help

Add the two expressions 3.8b - 7 and 2.9b + 9 enter your answer in simplified form

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)

9/10 divide by -3/15 as a mixed number