Hi , i am stuck on the algebra homework and i really don't get questions nine and the one with 21 matches, can you guys me?

8.
a) To find how many matches are used to make shape 9, you substitute 9 in as n, so your equation looks like
m = (4 × 9) + 1
m = 36 + 1
m = 37
So the amount of matchsticks is 37

b) Now we can substitute in 21, but place it where m is, so we get:
21 = (4 × n) + 1
- 1
20 = 4 × n
÷ 4
5 = n
So your answer is shape number 5.

9. You can write this out as an equation:
(6 × l) + (8 × p) = 640
Because you know that each letter is 100, you can substitute 100 in for l and get
(6 × 100) + (8 × p) = 640
600 + (8 × p) = 640
- 600
8 × p = 40
÷ 8
p = 5
So each pen is 5g.

I hope this helps!