I know this is a lot of questions but i don't understand please help

Answer:
21.C
23.B
24.D
Step-by-step explanation:
Domain is x
Range is y
If you can find a relation between x and y, that relation is a function.
In 21,
I. y = 0.x +5
II. Nothing.
III. y = x
In 22,
15 birdhouses needed to be built, then domain is from 0 - 15
In 23,
Try to insert x in to f(x) you will find out f(x), for i.e : x = 0, f(x) = 0.10 x 0 +5 =5.
Answer:
21. C
22. B
23. D
Step-by-step explanation:
21. For a function, every input must have a unique output so II is not a function
22. Domain is the no. of bird houses: 0 to 15
Range is the time: (0×20) to (15×20)
23. No. of apples is whole numbers
First x value is 0
f(0) = 0.1(0) + 5 = 5