How do i solve inequalities like this?

The circumference of a circle is 5 pi cm. what is the area of the circle?

Answer this question! 30 points and brainliest!

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)