Can you correct this 1st year Maths test to check if my answers are correct

OK. I am an adult and I am trying to help my kid with her Maths as her level is pretty low and needs help understanding her errors. However, I've never been an ace in Maths (I used to be pretty bad at her age) but since I've been trying to better myself in order to help her. It worked in Primary school. But now in Secondary school or Middle School the level is higher. Thanks in advance for your help! Here is the test she failed at:

1. Show that the factors of 28 excluding itself add up to 28. (My answer: 1, 2, 4, 7, 14)
2. Find the lowest common multiple of 6 and 8. (My answer: 2)
3. Find the highest common factor of 12 and 18. (My answer: 216)
4. In a faraway galaxy, 3 planets are lined up around a giant sun. They have orbits of 4, 6 and 10 years, respectively.
a) After how many years will the 3 planets be in line? (My answer: 2 years)
5. Tom was born on the first of January in the year
2² x 3² x 5 x 11. What age in full years is he now? (My answer: the year is 1980, and Tom is 32 years old in 2012)
6. A rectangular board measures 40cm by 24cm. What is the largest size square tiles that can be used to cover the floor without having to cut any tile? (My answer: 480cm)
7. A diver was at -65 metres. A shark was 8 metres below him. The diver rose 16 metres and the shark rose 12 metres. How far apart are the diver and the shark now? (My answer: 14 metres apart)
8. Calculate each of the following:
(a) 8 + ( -12 - 3) - ( -2 + 3) (My answer: -8)
(b) 2( -3 - 2)² - 4( -6 / 3)² + 8( -1)⁴ (My answer: -18)

1. error: must show factors=28
2. error: found lowest common factor
answer: 24
3. error: found a number with 12 and 18 as factors
answer: 6
4. answer: 60 found by finding lowest common multiple
5. correct
6. answer: 8cmx8cm tiles
need to find largest common factor of both length and width
7. answer: 12m apart
24m difference after diver swam up. 24-16=12 for shark rising