Interpret the pulley system

Let the heavier box be $m_2=8\,\text{kg}$ and the lighter box be $m_1=2\,\text{kg}$.

Since the string is massless and pulleys are smooth, this is an ideal Atwood-type system.

Find the acceleration of the system

The net driving force is due to the difference in weights: $F=(m_2-m_1)g=(8-2)\times 10=60\,\text{N}$

Total mass of the system: $m_1+m_2=2+8=10\,\text{kg}$

Therefore, acceleration is $a=\frac{F}{m_1+m_2}=\frac{60}{10}=6\,\text{m/s}^2$

Use kinematics to find time

Starting from rest, if the $8\,\text{kg}$ box falls a distance $s$, then $s=\frac{1}{2}at^2$

From the figure/data implied in the question, the $8\,\text{kg}$ box is initially $0.48\,\text{m}$ above the ground. So, $0.48=\frac{1}{2}(6)t^2=3t^2$

$t^2=\frac{0.48}{3}=0.16$

$t=0.4\,\text{s}$

Match with options

$t=0.4\,\text{s}$

So the correct option is D.

Comparison with stored answer

Stored correct answer: D
Derived answer: D
They agree.