People with health and fitness goals often monitor their weight category based on their height. Figure 1 shows a graph used to find if an adult's body mass is healthy for their height.

![A graph showing weight categories of adults based on height on the vertical axis, from 1.5 to 2.0 m with horizontal grid lines every 0.05 m, and body mass on the horizontal axis, from 40 to 160 kg with vertical grid lines every 5 kg. The graph is divided into four regions from left to right:

1. 'Underweight': The region to the left of the first boundary line. This boundary line starts at (40 kg, 1.48 m), passes through (54 kg, 1.72 m), (60 kg, 1.80 m), and (67.5 kg, 1.90 m).
2. 'Healthy weight': The region between the first and second boundary lines. The second boundary line separating 'Healthy weight' and 'Overweight' passes through (57 kg, 1.51 m), (72.5 kg, 1.70 m), (81 kg, 1.80 m), and (90 kg, 1.90 m).
3. 'Overweight': The region between the second and third boundary lines. The third boundary line separating 'Overweight' and 'Obese' passes through (68 kg, 1.51 m), (87 kg, 1.70 m), (97 kg, 1.80 m), and (108 kg, 1.90 m).
4. 'Obese': The region of body masses to the right of the third boundary line, up to 160 kg.](https://assets.mathsgenie.co.uk/aqa-qb/47f34628-c7bd-4785-bb42-2911c8ae0a0a.png)

An adult is $1.8m$ in height.