Brain Teaser August 2018 Answer

Sarah and Todd spray on the inhibitor on day 29, they gained just one extra day buying two ground cover stems. It would seem that buying two stems would cut the growing time in half, filling in all the dirt in just 15 days. But, the extra stem gives just them just one extra day before the cars and coffee. Remember, planting one stem on the first day results in it doubling in size the second day, which is what you got on the first day, planting two stems.