The independent variable (x) is the domain
Answer:
surface area of the triangular pyramid
=(1/2×9×7.8)+(3×1/2×9×12.3)
=35.1+166.05
=201.15 inch²
$1.88 is our amount after the 380% is added!
$1.88 - 380%*x = x
Note, that when you are working with percents in a problem you need to convert the percent into a decimal value in order to properly work with it in an equation like the one above.
So, it will look like this:
$1.88 - 3.8x = x
Now onto explaining how I derived this equation in the first place, because it doesn't help you if you don't know how to do it yourself.
How a percent problem works is if you are taking some original price x, and increasing it by 380% you would take 380% of the item, and then adding it to the item. To take 380% of an item you would need to multiply the number by 380% (3.8). So, if you translate that into math it looks like this:
x + 380%*x = y
Y, in this case is $1.88. In other words it is the price AFTER you've added 380% to the cost. So I started to solve for x by subtracting 380%*x on both sides leaving us with this:
$1.88 - 3.8x = x
We need to solve the equation for x by adding 3.8x on both sides.
$1.88 = 3.8x + x
Combine like terms.
$1.88 = 4.8x
Divide both sides by 4.8.
$1.88/4.8 = x
So our original price is $1.88/4.8!
The question asks for the 380% * x part of the problem.
So we take our answer and multiply it by 3.8.
($1.88/4.8)*3.8 = $1.49 mark up!
