Answer:
The answer is 8.88; You look at the number that comes after the second number (the second place after the decimal) and if that number is 5 or above then you round the second number up. (Sorry if it doesn't make sense, but that's the best I can explain it).
X-12=20
x=20+12
x=32
answer is 32
V = length times width times height
V = 45 * 12 * 10
V = 5400
Hope this helps
#1.
Here what you do is cross multiply.

#2.
Same as #1, just cross multiply.

You get the gist?