Final answer:
A wave with a wavelength of 3.0 m and a frequency of 25.0 Hz has made 501.4 complete oscillations at t = 20.0 s and x = 4.2 m.
Step-by-step explanation:
A wave cycle consists of one complete wave starting at the zero point, going up to a wave crest, going back down to a wave trough, and back to the zero point again. The wavelength of a wave is the distance between any two corresponding points on adjacent waves. In this case, the wavelength of the wave is given as 3.0 m.
The frequency of a wave is the number of waves that pass a certain point in a specified amount of time. In this case, the frequency of the wave is given as 25.0 Hz.
The number of complete oscillations a wave has made can be calculated by multiplying the frequency of the wave by the time. At t = 20.0 s, the wave has made 25.0 Hz x 20.0 s = 500 complete oscillations. At x = 4.2 m, the wave has made 4.2 m / 3.0 m = 1.4 complete oscillations.
Therefore, at t = 20.0 s and x = 4.2 m, the wave has made 500 + 1.4 = 501.4 complete oscillations.