First one
When 6 + 4i is multiplied by 3, the result is 18 + 12i. Graphically, this shows that the product is a scalar of the complex number.
Second one
Converges (gets smaller and smaller)
Geometric and the absolute value of the common ratio is less than 1 (=2/3)
Last one
The limit is just the ratio of the coefficients on the n^4 terms in the numerator and denominator = 2/6 = 1/3
