Answer:
This is an improper fraction so we need to make it a mix fraction.
Step-by-step explanation:
21/10 = 10/10+10/10+1/10
10/10=1
So your final answer will be 
You would divide the new bikes by four to find out the amount of used bikes
so 15
add them both then you get the awnser if the four is not a negative. if the four is a negative use division.
Answer:

C.E.: x <em>=/=</em> -4
Step-by-step explanation:

5=red
1/3 of all=red
1/3 of all=5
3/3 of all=all=1/3 times 3/1=5 times 3/1=15
15 total