that’s not bad for a start… and you also mostly followed the naming conventions…
a better name for Numberwithpowerof would be NumberWithPowerOf...
in the MIT App Inventor community there is no such thing as an extension developer group...
there is an extension developer group in Kodular... however imho to earn the developer badge you should provide something really useful, which is not possible with current blocks
and as we can see from the colors, you are using Kodular... so what about testing your extension if it is also working here in App Inventor and provide App Inventor screenshots?
btw are you aware, that there already exists a Math extension, which is able to calculate "everything"? And it only needs one method to do that...
But your extension may not be able to determine both values (x1,2) of a quadratic equation.
Or does it?
Then my extension would be superfluous. Wouldn't be tragic as it was only a first test for me anyway. My first extension - quadratic equation