How much power does this study have to detect a mean difference of 5 units in the symptom scale if a two-sided test is used with α = .05? 

Neurology

In a 5-year follow-up of bilateral stimulation of the subthalamic nucleus among 49 patients with advanced Parkinson’s disease, investigators assessed changes in symptoms as measured by the Unified Parkinson’s Disease Rating Scale (range = 0 to 108, with higher values denoting more symptoms). Assume this measure follows a normal distribution. The mean score at baseline was 55.7. The standard deviation of change from baseline to 5 years was 15.3.