Wires, temperature and the colour code

You will write three functions that a designer of resistors might use.

The idea. A round wire has $R = \rho L/A$ with $A = \pi d^2/4$. A metal has $R = R_0[1 + \alpha(T - T_0)]$. A carbon resistor shows two digits, a power of ten and a tolerance in coloured bands.

Your tasks.

1. In wire_resistance, return the resistance in ohm of a round wire. The resistivity is in ohm metre, and the length and diameter are in metres.
2. In resistance_at, return the resistance at the new temperature. The reference temperature is 20 degrees Celsius.
3. In decode, bands is a list of colours such as ["red", "red", "brown", "gold"]. Return the value in ohm and the tolerance in per cent. With only three bands the tolerance is 20.