How do you solve X^-3 x X^-5

Find the length of the following tangent segments to the circles centered at o and o' whose radii are 5 and 3 respectively and the distance between o and o' is 12. what is the tangent segment of cd?

Given f(x)= 9x+1 and g(x)=x^3, choose the expression (f*g)(x)

Which of these numbers of simulations of an event would be most likely to produce results that are closest to those predicted by probability theory? 15, 20, 5, 10