The last section is not correct the answer should be

2. 90 is 1/10 of what ? : 
    90 = 1/10x...multiply both sides by 10, this eliminates the 10 on the right
    90 * 10 = x
    900 = x <===
4. 5000 is 1/10 of what ? :
    5000 = 1/10x ...multiply by 10
    5000 * 10 = x
    50,000 = x <===
8. 2000 : 10 times as much = 20,000 : 1/10 as much = 1/10(2000) = 200
9. 400 : 10 times as much = 4000 : 1/10 as much = 1/10(400) = 40
10. 60 : 10 times as much = 600 : 1/10 as much = 1/10(60) = 6
12. u got it correct..it is 30,000

Neither is the answer