Five days after a tomato plant was planted, it measured 12.5 inches tall. Seven days after it was planted, it measured 15 inches tall. If the rate of growth remained constant, what is the most reasonable starting height of the plant?

We know that from day 5 to day 7 (2 days) the plant few 2.5 inches. That means it grew 1.25 inches a day. It states growth in constant. If the plant was 12.5 inches tall on day 5 and grew 1.25 inches a day ... in 5 days it grew 6.25 inches. (5 * 1.25). Day 5 it is 12.5 inches - the 6.25 = 6.25. Starting height was 6.25.