An ungraduated mercury thermometer is stuck to a 30 centimetre ruler, alongside the scale. The readings on the scale when the thermometer is at 0.0°C and 100.0°C are 36 mm and 61 mm respectively. The length of the mercury column varies linearly with temperature.
What is the temperature when the mercury is at the 43 mm mark?
A. 4°C
B. 72°C
C. 58°C
D. 28°C