1. The problem gives a histogram with frequency density on the y-axis and height intervals on the x-axis. We know 26 plants have a height less than 20 cm. 2. The total number of plants in each height interval is the area of each bar in the histogram, calculated as frequency density \( \times \) class width. 3. For the first interval (0 to 20 cm), the frequency density is approximately 1.3 and the class width is 20 cm. 4. Calculate the number of plants in the first interval: $$\text{Number} = 1.3 \times 20 = 26$$ This matches the given number of plants less than 20 cm. 5. Calculate the number of plants in the other intervals: - Second interval (20 to 40 cm): frequency density = 3.0, width = 20 $$3.0 \times 20 = 60$$ - Third interval (40 to 60 cm): frequency density = 2.5, width = 20 $$2.5 \times 20 = 50$$ - Fourth interval (60 to 80 cm): frequency density = 1.5, width = 20 $$1.5 \times 20 = 30$$ 6. Add all the plants to find the total number: $$26 + 60 + 50 + 30 = 166$$ 7. Therefore, the total number of tomato plants is 166.