MathNet 2018-part-07 — 177 problems (EN–VI) Question 142

$H O W$, $B O W$, and $D A H$ are equilateral triangles in a plane such that $W O = 7$ and $A H = 2$. Given that $D$, $A$, $B$ are collinear in that order, find the length of $B A$.