With these questions, the best approach is to draw a diagram to represent the question. Draw a right angle triangle with an angle of elevation 29 degrees (make sure to label the angle that meets the base and hypotenuse as 29 degrees).
From here, we say that the hypotenuse is the slide itself, which is 5.4 metres. Using basic trigonometric ratios, we can deduce that:
sin(29) = x/5.4
x = 5.4sin(29) which is approximately 2.62 metres.