two angles across from each other at a junction, are vertical angles, and therefore twins.
in this case, ∡7 and her twin ∡5 are each then 2x + 15, and ∡8 and her twin ∡6 are each 3x.
keeping in mind that in a circle, there is a total of 360°, so all those 4 folks will need to sum up to 360°.
[tex] \bf \stackrel{\measuredangle 7}{(2x+15)}+\stackrel{\measuredangle 5}{(2x+15)}+\stackrel{\measuredangle 8}{(3x)}+\stackrel{\measuredangle 6}{(3x)}~~=~~360
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10x+30=360\implies 10x=330\implies x=\cfrac{330}{10}\implies \boxed{x=33}
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\measuredangle 7=2(33)+15\implies \measuredangle 7=81 [/tex]
