What is the value of a and b f(x)=x(x+a)(x-b)

Unfortunately, Tashara, you have not provided enuf info from which to calculate the values of a and b.  If you were to set  F(x)=x(x+a)(x-b)  = to 0, then:

x=0,
x=-a
x=-b

but this doesn't answer your question.
Double check that you have shared all aspects of this question.

The answer is a hoped that