For the numeric part, you'll have to find the GCD of 15 and 25, which is 5. So, we can factor a 5 and we have
[tex]5(3s^{11}-5s^4)[/tex]
As for the literal part, you can factor [tex]s^4[/tex] because it's the power of s with the smallest denominator. So, we have
[tex]5s^4(3s^7-5)[/tex]
