Answer:
To find f-¹(x) of f(x) equate f(x) to y
That's
f(x) = y
So we have

Next interchange the variables that's x becomes y and y becomes x
That's

Next make y the subject
Cross multiply
We have
4y - 7 = 10x
Move -7 to the right side of the equation
4y = 10x + 7
Divide both sides by 4
We have the final answer as

So

Hope this helps you
Answer:
n = -1
Step-by-step explanation:
you've accidently substracted 6n from 12n when you were supposed to be adding them. (-6n becomes +6n when brought to the otherside of the equal sign)
I made this graph for you- the red is the 80%, and the green is the leftover 20%.
As we can notice the shape is a Pentagon. A Pentagon's angles should add up to 540. So we can use simple addition and subtraction to solve.
121 + 108 + 102 + 100 = 431
540 - 431 = 109
109 should be your answer