7. A. -18 cm, because it changes -3 cm/per year, so multiply 6 years by -3 cm to get -18 cm
8. D. $20, because it rose +$2 over 10 days, you multiply 10 days by $2 to get $20 total
No, it does not equal 0. Lets multiply it out and see what it actually equals.
15/25 * 25/15
15*25 / 25*15
375 / 375
Anything over itself is 1, so the final answer for the multiplication is 1.
The 2 {} you have are called sets. The union is what the 2 sets have in all.
You can think of this as you have green blue yellow cards. and your friend have green orange red cards. What colors do you have if you combine your cards.
Now that's just an example, in the question's case is what numbers does the 2 sets have in total.
Therefore the union of these 2 sets are {9,10,11,13}
Hope it helps!
