can someone please explain how to solve these questions?

The number of mold spores in a petri dish increases by a factor of 10 every week. If there are initially 40 spores in the dish, how long with it take for there to be 2000 spores?

and

The astronomer johannes kepler determined that the time, D, in days, for a planet to revolve around the sun is related to the planet's average distance from the sun, k, in millions of kilometres. This relation is defined by the equation log D = (3/2)logk - 0.7. Estimate the period of revolution of uranus about the sun, given its distance from the sun. Uranus is 2854 million kilometres away from the sun