Answer:

Step-by-step explanation:
x and 3x are on a straight line together. Therefore, they are supplementary and must add to 180 degrees.
Add x and 3x, and set that equal to 180.

Combine like terms on the right side of the equation. Both x and 3x have a variable, so they can be added together.


Since we want to find x, we have to isolate x. x is being multiplied by 4. The inverse of multiplication is division. Divide both sides of the equation by 4.



x is equal to 45, so the correct answer is B. 45
Answer:
$1876.31
Step-by-step explanation:
The present value can be found using the compound interest formula.
<h3>Present value</h3>
The formula for the future value of an investment of P earning annual interest rate r compounded n times per year for t years is ...
FV = P(1 +r/n)^(nt)
Filling in the known values gives ...
4000 = P(1 +0.085/4)^(4·9) = P(1.02125^36)
Then the amount to be invested is ...
P = 4000/1.02125^36 ≈ 1876.31
The present value is $1876.31.
Answer:
There are 30 books in the shelf.
Step-by-step explanation:
To solve this problem we can use a rule of three in such a way that 12 paperback mysteries are related to 40% of the books in the shelf in the same proportion that "x" total books are related to 100% of the books in the shelf. So we have:
12 -> 40%
x -> 100%
40*x = 12*100
40*x = 1200
x = 1200/40
x = 30 books
There are 30 books in the shelf.