Please I need help to solve those problems:
A) (+4) + (-7) multiply (-3)-(+5)

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)

School has 204 sixth grade students. if the sixth grade is 30% of the total school, how many students are in the middle school?

Rectangle bcde is similar to rectangle vwxy. what is the length of side vy? a) 1 7 b) 2 7 c) 3 7 d) 4 7