The response from the other tutor is exceedingly long and wordy, making it hard to follow.
In the last few lines of that response, he gets to the basic process of converting units.
To change units without changing a measurement, multiply by a "unit fraction" in which the numerator and denominator are equal measurements but in different units.
For a simple example....
12 inches 4*12
4 feet * --------- = ---- = 48 inches
1 foot 1
The units "cancel" resulting in a measurement in different units.
In this problem, you are given the value of 100 Euros in several currencies. So the ratio of any two of those numbers is a unit fraction.
(1) 45 pounds in rubles: multiply by rubles/pounds
4239 rubles
45 pounds * ------------
89.9 pounds
(2) 100 Australia dollars in Euros: multiply by Euros/Australia dollars
100 Euros
100 Australian dollars * ------------------------
143.2 Australian dollars
(3) 48 Australian dollars in US dollars: multiply by US dollars/Australian dollars
133.8 US dollars
48 Australian dollars * ------------------------
143.2 Australian dollars
You can do the calculations.