A student uses a transmission electron microscope at a magnification of ×30,000\times 30,000×30,000 to study the ultrastructure of a liver cell. They obtain the micrograph of a mitochondrion shown below.
On a printed copy of the micrograph, the student measures the length of the line X−YX-YX−Y across the mitochondrion to be 7.8 cm7.8\text{ cm}7.8 cm.
a.[1]
Convert the measured length of the line X−YX-YX−Y on the paper into micrometres (μm\mu\text{m}μm).
b.[2]
Calculate the actual (real) length of this mitochondrion in micrometres (μm\mu\text{m}μm). Show your working.