The Gravitational Potential Energy can be calculated using: GPE = m · g · h where
GPE will be joules if m = mass (in kilograms)
g = gravitational constant (9.8 m/sec²)
and h = height in meters.
The mass is 100 g = 0.1 kg and h = 1.75m: GPE = m · g · h = (0.1kg) · (9.8m/sec²) · (1.75m)
If you finish the calculation, you will have the answer.
Here is a solution with humor. Lancelots Links unexplained maths solution is overkill for this question, but is correct.
http://web2.0calc.com/questions/how-do-you-find-local-gravitational-potential#r2