Answer:

Step-by-step explanation:
(This exercise is presented in Spanish and for that reason explanation will be held in such language)
El lado restante se determina por la Ley del Coseno:



Finalmente, el angulo C se halla por medio de la misma ley:




Step-by-step explanation:
Refer to the attachment.
I hope it helps:)
B)subtraction hopes this help:)