Let x be a number of skateboards and y be the number of bicycles in Eddie's repair shop. 
Eddie asks the girls to order 54 new wheels for 21 skateboards and bicycles, then
x+y=21.
One scateboard has 4 wheels, then x scateboards have 4x wheels, one bicycle has 2 wheels, then y bicycles have 2y wheels. In total there should be ordered 54 wheels, so
4x+2y=54.
Solve the system of equations:

From the first equation  Substitute it into the second equation:
 Substitute it into the second equation:

Then

Answer: 6 scateboards and 15 bicycles.
 
        
             
        
        
        
The two numbers are 12 and 16. 12 + 6 = 18. 6 doubled is 12. 12 plus 6 equals 18. 
        
             
        
        
        
BC = 6 km
<u>/</u><u> </u> ACB = 34° 
AC = ?
cos 34° = 
=> 0.829 = 
=> AC = 
=> AC = 7.23763570567
=> AC = 7 km 
=> AC = 10 km (nearest tenth)
 (nearest tenth)

<h3>Answer : 10 km</h3>

HOPE IT HELPS
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Answer:
First answer: "Add the exponents" 
Step-by-step explanation:
The laws of exponents include the following for product of exponents with the same base:

which implies addition of exponents
So you need to add exponents