Answer
$69$
Work Step by Step
$a_1=-7$ and we can see that the difference of subsequent terms is $4$, thus $d=4$
The nth term of a geometric sequence can be obtained by the following formula: $a_n=a_1+(n-1)d$, where $a_1$ is the first term and $d$ is the common difference.
Hence here: $a_{20}=-7+(20-1)\cdot(4)=-7+76=69$
