Rb = Vbc / Ib

150 Ib = Ic = 0.0015
で Ic = 0.0015だから
Ib = 0.0015 / 150 = 0.00001

Vbc = 16 - 4000 Ie - 0.6 = 16 - 4000 * (0.0015 + 0.00001) - 0.6
Vbc = 16 - 6.04 - 0.6 = 9.36

よって
Rb = 9.36 / 0.00001 = 936k