#### Answer

$a_4 = \dfrac{24}{25}$

#### Work Step by Step

To find the fourth term, the value of the common ratio $r$ is needed.
The value $r$ can be found by dividing the second term by the first term of the sequence.
Thus,
$r=\dfrac{a_2}{a}
\\r=\dfrac{6}{15}
\\r=\dfrac{2}{5}$
The fourth term can be found by multiplying the common ratio $r$ to the second term twice:
$a_4 = a_2 \cdot r \cdot r
\\a_4 = 6 \cdot \dfrac{2}{5} \cdot \dfrac{2}{5}
\\a_4 = \dfrac{24}{25}$