A ratio of 5:7 means out of 12 books, 5 are in one category and 7 are in another. (The “category” isn’t specified in this problem.)
So here we’re STARTING with 36 books; we want to find a ratio that is equal to 5:7 and adds up to 36. Well 36 = 3(12), and so if we multiply each number in the ratio by 3 as well, we might get what we want. Doing that gives us 15:21, which adds up to 36 and is equal to 5:7. Boom, that’s the answer.
P.S. Here’s a question you can think about: why do ratios stay the same when you multiply each number by the same amount? (For example, why is 3:1 the same as 6:2?)
Answer:
A
Step-by-step explanation:

Hope this helps!
Answer:

Step-by-step explanation:
The open circle means that the point is not included in the solution set, and the arrow pointing left means that all numbers less than -2 are members.
In set-builder notation, each term has a special meaning. The braces enclose the members of the set.
Here's how you translate the notation,

To find the box to the top left, we can multiple the sides like rectangles. To find the top left box, we can multiply -1 and 0.5y to get -0.5y.
To find the box on the bottom right, we can multiply the sides like rectangles again. To find the bottom right box, we can multiply 24x and 3 to get 72x.