So the easiest way to solve this is to use the straight line provided .
180=90+61+x
180=151+x
29=x
        
                    
             
        
        
        
5.476 rounded to the hundrdths is 
5.48
        
                    
             
        
        
        
You need to put everything to one side and equal to 120. Then you combine all like terms. 
then you subtract 24 with 120. You get 94/24=4
10x+6x+16+8x+8=120
24x+24=120
 -24 -24
____________
24x=96
/24 /24
 X=4
        
             
        
        
        
The complete question is
<span>Sarah rides her horse for 2 1/6 hrs with a constant speed of 6 km/hr and then for another 2 hours and 5 minutes with a constant speed of 12 km/hr what is her average speed for the total trip?</span>
we know that
speed=distance/time
1) Sarah rides her horse for 2 1/6 hrs with a constant speed of 6 km/hr
time=2 1/6 hrs----> 13/6 hrs
speed=6 km/h
distance=speed*time----> 6*(13/6)---> 13 km
2)for another 2 hours and 5 minutes with a constant speed of 12 km/hr
time=2hrs+5 minutes----> 2+(5/60)--> 125/60 hrs
speed=12 km/hrs
distance=speed*time----> 12*(125/60)---> 25 km
3) find the average speed for the total trip
total distance=13 km+25 km----> 38 km
total time=(13/6)+(125/60)----> (10*13+125)/60----> 4.25 hours
speed=38/4.25----> 8.94 km/hrs
the answer is
8.94 km/hrs