Answer:
100°
Explanation:
You want the missing arc measure in the geometry where two chords cross at 85° and they intercept one arc of measure 70°.
Crossing chords
The angle where chords cross is the average of the two arcs that they intercept. Here, that means ...
85° = (AE +BC)/2
Solving for BC, we get ...
2(85°) = AE +BC
BC = 170° -AE = 100°
The missing arc measure is 100°.