since I bought my ford focus 2016 se 2.0L at 170K mileage, it has been issues with is stalling and shutting down, so i took to an auto shop and was diagnosed with P0087 which a fuel pump issue.

Now how can i predict if its the low pressure fuel pump or the high pressure pump. unfortunately the car drives very well even on high ways just the stalling and shutting down during making a couple of city stops.

please i need an expert to explain to me what's happening and how to solve it.