You can enter this into the website calculator: http://web2.0calc.com/
Be careful with parentheses; this question could be written as:
A) $${\left(-{\mathtt{3}}\right)}^{{\mathtt{8}}} = {\mathtt{6\,561}}$$
or B) $${\mathtt{\,-\,}}\left({{\mathtt{3}}}^{{\mathtt{8}}}\right) = -{\mathtt{6\,561}}$$
It depends on whether negative 3 is the number being taken to the 8th power, or whether the question is asking for negative (3 to the 8th power).