If m∠AOB is 60° then m∠COB must be 30° because the line is splitting the line in two equal parts. Since m∠COB = 30°, then m∠CBO = 60°, m∠COA = 30° and m∠CAO = 60°. So, the triangle AOB is equilateral as all interior angles are equal. Therefore, AB= 2*BC= 4, OB=4 and OA=4.