Respuesta :

(x^12)^5=x^(12*5)=x^60
(x^(-2))^9=x^(-18)
x^60*x^(-18)=x^(40) and we need to find x^a such that
x^(42)*x^a=x^(40)^5
x^a=x^(40)^5*x^(-42)
x^a=x^(200)x^(-42)
x^a=x^(200-42)
x^a=x^158
so the missing term is x^158