What's the decay factor of an exponential function that represents a 64% decrease?​

Grace is a 70-year old woman who paid the utility bill online for the first time. she called her bank's customer service center to make sure she had done the transaction successfully. but the voice recording repeatedly played a message that all representatives were busy, which irked grace. which factor would make grace not recommend the bank to others? a. absence of technology b. lack of accessibility c. lack of financial products d. poor reputation