Well the answer options are a bit confusing but the steps are 1, 2, & 3.
<span>{[(16 ÷ 4) × (2 × 6)] ÷ 6} + 4 =
</span><span>{[(4) × (12)] ÷ 6} + 4 =
</span>{[4 × 12] ÷ 6} + 4 =
{[48] ÷ 6} + 4 =
{48 ÷ 6} + 4 =
{8} + 4 =
8 + 4 =
12
It's evident that the first four terms are 4, 4/3, 4/9, and 4/27. So the fourth partial sum of the series is

It's as easy as adding up the fractions, but I bet this is supposed to be an exercise in taking advantage of the fact that the series is geometric and use the well-known formula for computing such a sum.
Multiply the sum by 1/3 and you have

Now subtracting this from

gives

That is, all the matching terms will cancel. Now solving for

, you
have

