The radius-times-turn product equals the stated arc length.
(x+8)(x−3)x2+5x−84(x+12)(x−7)=60,=0,=0.
The candidates are 7 and -12. The negative candidate gives a negative radius and turn. For x equal to 7, the radius is 15 cm and the turn is 4 radians, below one full turn; their product is 60 cm.