Answer: C. (5x+3)(5x+3)
Explanation:
This is assuming this is a quadratic with 25x2 actually being 25x^2
We can start by simplifying the 25 to be 5^2
As well as the 9 to be 3^2
The expression now looks like:

Now we can apply an exponent rule to the 5^2 x^2
The rule states:

So this means:

We can now rewrite 30x as 2 * 5x * 3
The expression now looks like:

Now this expression matches with the perfect square formula which states:

Our a value is 5x and our b value is 3.
So:

The answer is (5x+3)(5x+3)