a-3b/3x2+15xy

It seems like you're trying to simplify or factor the expression \(\frac{a - 3b}{3x^2 + 15xy}\).

First, let's look at the denominator \(3x^2 + 15xy\). We can factor out the greatest common factor, which is \(3x\):

\[ 3x^2 + 15xy = 3x(x + 5y) \]

Now, we can rewrite the original expression:

\[ \frac{a - 3b}{3x^2 + 15xy} = \frac{a - 3b}{3x(x + 5y)} \]

This expression is now simplified, but it cannot be simplified further unless additional information about \(a\) or \(b\) is provided.

If you have specific instructions or additional context for this expression, please let me know!