hello everyone i hope your all well

, anyway im new to the forum and need a little help solving some math problems i hope you can help me, first off im not very good at math and i have a hard time explaining the math so im sorry if i dont make much since but here it goes, basicly depend on the question i have to solve for either, A, a, B, b, C or c for either angle or degree if you under stand so far and i have some answered but the ones with the first angle and degrees to solve for the others confuses me here is an example

its the 18.7 with the others that confuses me, the way my teacher said to solve it, is like this,

, which is not even an answer, so if someone has an easier way to solve a problem like this where a number is like 18.7 (with the point 7 or point whatever) please let me know and step by step on how to solve it please and im really really sorry for the long post. thanks in advance.