To solve this problem we apply the kinematic equations of linear motion. For which the speed is described as the distance traveled in a time interval. This would be,
[tex]v = \frac{x}{t} \rightarrow t = \frac{x}{v}[/tex]
Our values are given as,
[tex]\text{The speed of the boat} = v_b = 3.8m/s[/tex]
[tex]\text{The speed of the ocean} = V = 6.8m/s[/tex]
[tex]\text{The wave length of the wave is the same distance traveled by boat} = d = \lambda = 30m[/tex]
[tex]\text{The relative speed of the boat} = v_r = -3.8 +6.8 = 3m/s[/tex]
Replacing we have,
[tex]t = \frac{d}{v_r}[/tex]
[tex]t = \frac{30m}{3m/s}[/tex]
[tex]t = 10s[/tex]
Therefore will take until the boat is next on a crest around to 10s
