This is the concept of indices. To re-write the question as instructed we proceed as follows:
b^-6×b^11
according to the rules of indices, when we multiply the number which have the same base, we add their powers. In our case this will be:
b^-6×b^11
adding their powers we get:
b^(-6+11)
=b^5
the answer will therefore be b^5
