We know that OB bisects EC where they intersect would be at point O,
so the two lengths EO and OC must be equal.
2x - 20 = 70 - x
[adding x + 20 to each side]
2x - 20 + x + 20 = 70 - x + x + 20
[simplifying]
3x = 90
[dividing each side by 3]
x = 30 would be the answer