A sample containing sulfur (atomic mass 32 u), manganese (55 u), and an unknown element is placed in a mass spectrometer. The ions all have the same charge and are accelerated through the same potential difference before entering the magnetic field. The sulfur and manganese lines are separated by 3.20 cm on the photographic plate, and the unknown element makes a line between them that is 1.07 cm from the sulfur line.
What is that mass of the unknown element in u?