Figure shows two block system, \( 4 \mathrm{~kg} \) block rests on ...

Figure shows two block system, \( 4 \mathrm{~kg} \) block rests on a smooth horizontal surface, upper surface of \( 4 \mathrm{~kg} \)
\( \mathrm{P} \) is rough. A block of mass \( 2 \mathrm{~kg} \) is placed on its upper surface. The acceleration of upper block with respect to earth when \( 4 \mathrm{~kg} \) mass is pulled by a force of \( 30 \mathrm{~N} \), is
(1) \( 6 \mathrm{~m} / \mathrm{s}^{2} \)
(2) \( 5 \mathrm{~m} / \mathrm{s}^{2} \)
(3) \( 8 \mathrm{~m} / \mathrm{s}^{2} \)
(4) \( 2 \mathrm{~m} / \mathrm{s}^{2} \)