I don't know how you expand it but the answer is 3x + 25 unless that's expanding.
The second choice is the answer
I'm guessing the series is supposed to be

By the ratio test, the series converges if the following limit is less than 1.

The first

terms in the numerator's denominator cancel with the denominator's denominator:


also cancels out and the remaining factor of

can be pulled out of the limit (as it doesn't depend on

).

which means the series converges everywhere (independently of

), and so the radius of convergence is infinite.
X ·2 = 12x - 15
2x = 12x - 15
2x + (-12x) = (12x - 15) + (-12x)
Result: x = 3/2
13
14=2•7
15=3•5
16=2•2•2•2
17
18=2•3•3
19
20=2•2•5
...