Answer:
15.02 m/s.
Explanation:
Given that the height of the hill, h= 11.5 m.
Combined mass, m= 54.8 kg
The initial velocity of the combined mass, u=0
Acceleration due to gravity,
.
Angle of the path the horizontal,
degree.
Let A be the initial position and B be the final position of the sled as shown in the figure.
The path is frictionless so the drag force =0
The gravitational force acting on the combined mass in the downward direction, 
The component of force acting in the direction of motion = 
Let
be the acceleration of the combined mass, m, So,

[ from equation (i)]

Let v be the final velocity of the combined mass.
Now, by using the equation of motion,

Here, s is the displacement in the direction of motion,
So, s= AB
Now, in the right-angled triangle ABO,

Now, from equations (ii), (iii) and (iv), we have

By using the given values, we have

Hence, the speed of the combined mass at the bottom = 15.02 m/s.