Evaluate (80/640)^(-2/3)

$$\frac{80}{640} = \frac{8}{64} = \frac{1}{8}$$

So the expression becomes:

$$\left(\frac{1}{8}\right)^{-\frac{2}{3}}$$

A negative exponent means taking the reciprocal of the base.

$$\left(\frac{1}{8}\right)^{-\frac{2}{3}} = \left(\frac{8}{1}\right)^{\frac{2}{3}} = 8^{\frac{2}{3}}$$

The exponent $\frac{2}{3}$ means taking the cube root first, then squaring the result.

$$8^{\frac{2}{3}} = \left(\sqrt[3]{8}\right)^2$$

$$\sqrt[3]{8} = 2$$

So the expression becomes:

$$(2)^2$$

$$(2)^2 = 4$$

The evaluated value is 4.