Percent error = (estimate - real)/(real) * 100
percent error = (78.25 - 75.50)/(75.50) * 100
percent error = 3.6%
There is no m in the diagram showed
For this case we have an equation of the form:

Where,
h0: initial height
v0: initial speed
a: acceleration
Substituting values we have:

Rewriting we have:

Note: see attached image
Answer: