To solve this, create an equation that follows 45% of a value is 18. This would look like x*.45=18. Now, solve for x, x*.45=18, divide by .45, x=18/.45=40, making your value 40. To check, plug in your value to the equation 40*.45=18 and see if it stays true.
The only way to solve if it is equal to something
assuming that the teacher wanted you to make it equal to zero do
0=-3x^2-21x-54
remember if we can do
xy=0 then assume x and y=0
so factor
0=-3x^2-21x-54
undistribute the -3
0=-3(x^2+7x+18)
remember 0 times anything=0 so
x^2+7x+18 must equal zero
use quadratice formula which is
if you have
ax^2+bx+c=0 then
x=

x^2+7x+18
a=1
b=7
c=18
x=

x=

x=

i=√-1
x=

the zerose would be
x=

or
To the nearest thousand is 23,000 and the nearest ten thousand is 20,000
D. Because you're multiplying 3 by a number which is what the variable represents (n), then you're just adding 7 to that which equals 19 all together. It all translates to 3n+7=19.