ANSWER

Step-by-step explanation
We want to find the acceleration due to gravity on the moon.
To do this, we have to apply one of the equations of motion for a body falling freely under gravity:

where u = initial velocity
v = final velocity
g = acceleration due to gravity
t = time taken
Neil Armstrong dropped the hammer, so its initial velocity is 0 m/s:

We have to solve for g:

That is the acceleration due to gravity on the moon.