Basically all x^a functions have a roots. If you have less solutions than roots, then some roots are double or larger roots.

x^87=0 have 87 roots but 1 solution (namely 0), so that's one 87 root. Understand the concept, not my words (as they're probably described differently in the books).

They appear when a term is repeated (x+4)^3*(x-3)=0 have 4 roots and 2 solutions (-4, 3). Because the first term is repeated three times, -4 becomes a trippel root.
(aka full answer is -4, -4, -4, 3)

As I take it this is part of a test, I'll refrain from giving the correct answers.