How to divide a number by $2$ numbers?

I have to distribute newspapers, and the printing company gives it to me in bundles of $15$ and $25$, now if a store wants $115$ I will have to send them $4 \times 25$ and $1 \times 15$, or if they want $55$ I will send them $1 \times 25$ and $2 \times 15$.

And I would rather send bundles of $25$ then $15$, so if they ask for a $150$ copies, I want to send them $6$ bundles of $25$ and not $10$ of $15$.

Is there a formula to find the best combination of the $2$ bundle sizes to send to my customers?

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A sample algorithm could be: given $x$ denoting the newspaper number, you may want to maximise the 25 bundle, so you have to divide $x$ by 25: $x=25*A+r$. Then you have to divide $r$ by 15 so: $r=15*B+r_1$. If $_1$ is zero you can satisfy the request and you will have maximised the 25 bundle. –  7raiden7 Jul 2 '14 at 16:44
This is part of the Coin problem –  Ross Millikan Jul 2 '14 at 16:47

The lowest common multiple of 25 and 15 is 75. So assume the printing company gives a number $n$ that can be expressed as a finite sum of 25s and 15s. If $n$ is divisible by 25, then you are done. Otherwise, subtract by 15 until the result is divisible by 25. You will only need to subtract 4 times at the most because 75 is 15*5.