4. a) Determine if the credit card number 4147180124197779 has a correct check digit. Is this a Visa, Master or American Express card? b)Let g be a function from X to Y and let f be a function from Y...

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Extracted text: 4. a) Determine if the credit card number 4147180124197779 has a correct check digit. Is this a Visa, Master or American Express card? b)Let g be a function from X to Y and let f be a function from Y to Z, where X,Y and Z are sets. If the statement is true, prove it; otherwise, give a counter example. "If f and g are one to one and onto, the f • g is one-to-one and onto" c) If f (x) = 6 + 27x-1 is a bijective function, does the inverse exist? If yes, find the inverse otherwise explain why the inverse does not exist.