Answer:
Below!
Explanation:
f(x) = 2x/5x+6
Sub y for f(x) : y = 2x/5x+6
Swap x and y : x = 2y/5y+6
Multiply both sides by 5y+6 : 2y = (5y + 6) x
Distribute x : 2y = 5xy + 6x
Change sign : 2y - 5xy = 6x
Factor out y : (2-5x)y = 6x
Divide both sides by 2-5x : y = 6x/2-5x
Substitute for y : f^-1(x) = 6x/2-5x
Answer: f^-1(x) = 6x/2-5x
That's the best I could do with my current math knowledge, I hope it makes sense :)