Tính

giúp em giải hết nhen
$$\begin{gathered} a)3-{\left(-\frac{6}{7}\right)}^0+{\left(\frac{1}{2}\right)}^2 \\ b){\left(-2\right)}^3+2^2+{\left(-1\right)}^{20}+2^0 \\ c){\left({\left(3\right)}^2\right)}^2-{\left({\left(-5\right)}^2\right)}^2+{\left({\left(-2\right)}^3\right)}^2 \end{gathered}$$