The max value of the slope of the tangent line to the curve of f(x)= -1/3x^3+3x^2-5x I don’t understand how to work thru this question.

The max value of the slope of the tangent line to the curve of f(x)= -1/3x^3+3x^2-5x

I don’t understand how to work thru this question.

can someone explain step by step