1. Triangle $HJK$ is isosceles with $HJ=HK$ and $JK=\sqrt{80}$

$H$ is the point with coordinates $(−4,1)$
$J$ is the point with coordinates $(j,15)$ where $j<0$
$K$ is the point with coordinates $(6,k)$

$M$is the midpoint of $JK$.
The gradient of $HM$ is 2

Find the value of $j$and the value of $k$.