How can you determine the amount of voltage in one of the coils of a transformer?

Why do you assume that everybody knows what you are talking about?

If you are given figures for a hypothetical transformer, then you just calculate the numbers. You need to know how to do that to continue the course, and you should learn it perfectly. It's simple enough.

If you have an actual transformer you can measure the resistance of the coils to figure out which is the primary and what voltages you might expect on each coil. Then you would try to see the sizes of the wires to guess the current capacity. With that information you can apply some ac voltage to one coil and measure the outputs from other coils. Then you calculate the ratios.