When diving 4171 by 5000, you get the answer of 0.8342. If you are using a calculator, you can use a button that allows you to convert decimals to fractions and vice versa.
If you look at it, 2 of the angels are the same- those angels are A and B- the angel we are looking for. Angel A is 78 degrees and if angel A and angel B are equal then angel B is also 78 degrees.