Efficient algorithm?

Given an unlimited supply of coins of denominations x1; x2; : : : ;
xn, we wish to make change for a value v using at most k coins; that
is, we wish to find a set of k coins whose total value is v.
This might not be possible: for instance, if the denominations are 5
and 10 and k = 6, then we can make change for 55 but not for 65. what
is an efficient dynamic-programming algorithm for the following
problem.
Input: x1; : : : ; xn; k; v.
Question: Is it possible to make change for v using at most k coins,
of denominations x1; : : : ; xn?
any help would be appriciated.

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