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Answer 1 · 2018-01-19T11:29:39

#AB=CD~~10.8#
#BC=DA~~6.85#

So, we have this:
enter image source here

Since the two diagonal lines bisect each other, we know that #DE=EB=5.2# and #AE=EC=7.4#

The cosine rule tells us that #c^2=b^2+a^2-2abcosC#

#c=BC#
#a=BE=5.2#
#b=EC=7.4#
#C=/_BEC=63#

#BC=sqrt(5.2^2+7.4^2-2(5.2*7.4)cos63)~~6.85#

We can repeat this but with #C=117#

#CD=sqrt(5.2^2+7.4^2-2(5.2*7.4)cos117)~~10.8#