You have to begin by using the triangle sum therom. That means Angle DEC would be 64°, Angle D would be 76°, and angle C would be 40°
a= 6-2b-3c
then put that equation inside the first one and then the second one
you get -6*(6-2b-3c)+2b-3c=23
and 5*(6-2b-3c)+4b-3c=-12
14b-15c=59
14b-18c=18/*(-1)
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3b=41
S=((294+3)*(294/3))/2=14553
I believe that it is 24.99 but I'm not too sure. Anyways I hope I helped!