The measure of a central angle is equal to measure of a minor arc. That makes m<GEH=17x+12. By the Vertical Angles Theorem, m<GEH and m<IEF are equal to each other (m<GEH=17x+12=m<IEF). By the same theorem, m<FEG and m<IEH are also equal (m<FEG=8x-7=m<IEH). The angles in a circle must all add up to 360 degrees, 2(17x+12)+2(8x-7)=360. Solve for x, then plug x into the equation for m<IEF.
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