Answer
a). $1.815m/s^{2}$
b). $6.38N$
Work Step by Step
a). $T-m_{1}g=m_{1}a$
$m_{2}g-T=m_{2}a$
From above 2 equations, $a=\frac{m_{2}-m_{1}}{m_{1}+m_{2}}g$
$a=\frac{0.80-0.55}{0.80+0.55}9.8=1.815m/s^{2}$
b). So, $T=m_{1}(a+g)=0.55(1.815+9.8)=6.38N$