Two blocks are connected by a string as shown in the diagram. The upper block is hung by another string. A force $F$ applied on the upper string produces an acceleration of $2 \mathrm{~m} / \mathrm{s}^{2}$ in the upward direction in both the blocks. If $T$ and $T^{\prime}$ be the tensions in the two parts of the string, then $\quad$
(a) $T=70.8 \mathrm{~N}$ and $T^{\prime}=47.2 \mathrm{~N}$
(b) $T=58.8 N$ and $T^{\prime}=47.2 N$
(c) $T=70.8 N$ and $T^{\prime}=58.8 N$
(d) $T=70.8 N$ and $T^{\prime}=0$