The formula h -15 = 3.2t gives the height h in inches of a plant t weeks after planting. When was the height 31 inches?

To find out when the height of the plant was 31 inches, we can substitute this value into the given formula and solve for t. The formula h - 15 = 3.2t represents the relationship between the height of the plant (h) and the number of weeks after planting (t). Substituting h = 31 into the formula:
31 - 15 = 3.2t
16 = 3.2t

To isolate t, divide both sides of the equation by 3.2:
16 / 3.2 = t
5 = t

Therefore, the height of 31 inches was reached 5 weeks after planting.