Kris has an endless supply of 4-cent stamps and 7-cent stamps for mailing a package. what is the greatest amount of postage that cannot be affixed to a package using these stamps?

65

Explanation:

Using the addition table shown in the file attached:

Alternatively 4x + 7y can be an expression to solve this, with x = 4 and y=7

then we have 4(4) = 7(7)

= 16 + 49 = 65

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