Don't know which iterative method to use for specific x = f(x)

Question

I have this equation $$ f(x) = \sum_{k=0}^{n} {a_k x^k} + b*sin(nx) $$ for given $b,a_0,a_1,...,a_n$ ($n$ being dependant on haw many $a_k$ are there) and I have to solve $x=f(x)$ using an iterative method. The only problem I have is I don't know what method should I use. If someone could just give me the name of some method I could use here I would be grateful. Thanks.