Straighten a curve with a logarithm

You will take the logarithms of a set of counts, compare $r$ before and after, and turn the slope of the log line into a doubling time. The checker uses the yeast culture of the lesson.

The idea. If $\log_{10} y = a + bx$, the count grows by a factor $10^{b}$ for each unit of $x$, and it doubles every $\dfrac{\log_{10} 2}{b}$ units.

Your tasks.

1. Finish logs(values). Return the list of $\log_{10}$ of each value.
2. Finish doubling_time(xs, ys). Fit a line to the logarithms and use its slope.
3. Finish predict(xs, ys, x). Predict on the log scale, then undo the logarithm.