Okay, first let us expand it by doing the indicated multiplication...
-10+2√5-15√5+15 combining like terms we have:
2√5-15√5+5 notice that the constant 5 can be expressed as √5√5 so you have:
2√5-15√5+√5√5 since these all have the same √5 coefficient we can say:
(2-15+√5)√5
(√5-13)√5
5-13√5