Credit cards have 16 digit numbers, of which the first 15 digits identify the credit card and the sixteenth digit is the check digit (the last digit is fixed). u-kan-trust-us credit card numbers begin with 61, 62, or 63. what is the maximum number of credit cards that uktu can issue? latex: 3\left(10^{12}\right) 3 ( 10 12 ) 3 ( 10 12 ) latex: 3\: \left(10^{13}\right) 3 ( 10 13 ) 3 ( 10 13 ) latex: 3\left(10^{14}\right) 3 ( 10 14 ) 3 ( 10 14 ) latex: 3\left(10^{15}\right)