You can use your understanding of right triangle trigonometry to answer this question.

First let's label the height of the cliff as y, and the distance between the second boat and the bottom of the cliff as x. Now, you can set up two different questions, in terms of x and y, to describe the relationship between the angle created by the boat and the top of the cliff. We realise that the trig function you need to use is Tan, as you need to find Opposite over Adjacent.

Now, you have the following equations:
tan27 = y / (35 + x)
tan54 = y / x

Now solve these simultaneous equations, and you will end up with the answer for the height of the cliff as 28.3m