Do you mean:

x^5·e^(-3·ln(x)) + 4x = 21 ?

Do you see how the use of bracketing symbols makes the equation clear? Also, you should not mix uppercase and lowercase variable names, as these technically refer to different variables. Lastly, the natural log function is expressed as "ln" not "In."

Now, given that I have interpreted correctly this time, do you have any thoughts on what you should do first?