Answer
$\text { Applying Newton's second law to cab } B \text { (of mass } m)$ we have
$$
a=\frac{T}{m}-g=4.89 \mathrm{m} / \mathrm{s}^{2}
$$
$\left.\text { Next, we apply it to the box (of mass } m_{b}\right)$ to find the normal force:
$$
F_{N}=m_{b}(g+a)=176 \mathrm{N} \text { . }
$$
Work Step by Step
$\text { Applying Newton's second law to cab } B \text { (of mass } m)$ we have
$$
a=\frac{T}{m}-g=4.89 \mathrm{m} / \mathrm{s}^{2}
$$
$\left.\text { Next, we apply it to the box (of mass } m_{b}\right)$ to find the normal force:
$$
F_{N}=m_{b}(g+a)=176 \mathrm{N} \text { . }
$$
