help with some math problems ?

1)
5y/(5y + 15) ÷ 15y/(y + 3)
= 5y/5(y + 3) * (y + 3)/15y
= y/(y + 3) * (y + 3)/15y
= y * 1/15y
= y/15y
= 1/15

2)
6/(5x - 10) * (x - 2)/7x
= 6/5(x - 2) * (x - 2)/7x
= 6/5 * 1/7x
= 6/35x

3)
8a/3a * a/6a^2
= 8/3 * 1/6a
= 8/18a
= 4/9a

4)
7/3x * 3x/2x
= 7/3x * 3/2
= 7/x * 1/2
= 7/2x

5)
y/(6y + 8) * (3y + 4)/4
= y/2(3y + 4) * (3y + 4)/4
= y/2 * 1/4
= y/8

6)
(2x + 4)/x ÷ (3x + 6)/2
= 2(x + 2)/x * 2/3(x + 2)
= 2/x * 2/3
= 4/3x

7)
4y/x ÷ 8/x
= 4y/x * x/8
= 4y * 1/8
= 4y/8
= y/2

8)
4/5x * 1/5x
= 4/25x^2

9)
12/(m + 6) ÷ 9m/(2m + 12)
= 12/(m + 6) * 2(m + 6)/9m
= 4/(m + 6) * 2(m + 6)/3
= 4 * 2/3
= 8/3

10)
(6b + 18)/b ÷ (b + 3)/b
= (6b + 18)/b * b/(b + 3)
= 6(b + 3) * 1/(b + 3)
= 6

11)
4/(x + 2x - 8) * (x + 4)/8
= 4/(3x - 8) * (x + 4)/8
= 1/(3x - 8) * (x + 4)/2
= (x + 4)/2(3x - 8)

12)
a/10 ÷ 4a/5
= a/10 * 5/4a
= a/2 * 1/4a
= 1/2 * 1/4
= 1/8

12) a/10 divide 4a/5
(a/10)(5/4a)=1/8

8)
(4/5x)(1/5x) = 4/25x