Question

find the slope of the graph of the function y=(5x)/(3-x) at (4,20)

Answer 1

Differentiate the equation, and make it equal to zero, solve it and then plug in your values for x and y.

Answer 2

Really? At (4,20)? Your professor is super mature.

Answer 3

But here's how to solve it:
Using quotient rule
y' =[ 5(3-x) - (-1)(5x) ]/(3-x)^2
= [(15-5x) +5x] /[x^2 -6x +9]
=[15]/[x^2 -6x +9]
Substitute in x=4 and solve.