So you know that a circle has 360°, which means each side has to be 180°.
FC, the side with ∠1 has to be 180°
DC is 70°.
180 - 70 = 110.
This means that FD, the arc of ∠1, is 110° because it's a central angle, which has to be equal to the intercepted arc.
The answer is 110°.
