Answer:
He is 20 at oldest, or 
Step-by-step explanation:
The first step in finding a possible age is:
Subtract 10 from 51, and you get 41. Divide by 2, and you get about 20.5.
This means Joe is younger than or 20 years old.
Answer:

Step-by-step explanation:

When x = 4,

Answer:
Step-by-step explanation:
[0,7)
because the dot is colored in you need to have the bracket