The circle C1 with radius 6 and the circle C2 with radius 8 are externally tangent to each other at A. The circle C3 which is externally tangent to C1 and C2 has a radius with length 21. The common tangent of C1 and C2 which passes through A meets C3 at B and C. What is ∣BC∣? <spanclass=′latex−bold′>(A)</span>24<spanclass=′latex−bold′>(B)</span>25<spanclass=′latex−bold′>(C)</span>143<spanclass=′latex−bold′>(D)</span>243<spanclass=′latex−bold′>(E)</span>253