the sum of all interior angles in a polygon is
180(n - 2) n = number of sides in the polygon
so this one has 4 sides, so the sum of all those angles is 180(4 - 2) = 360, thus
[tex]10y+10y+9y+y~~ = ~~360\implies 30y=360\implies y=\cfrac{360}{30}\implies \boxed{y=12} \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\measuredangle J}{10(12)\implies 120}~\hfill \stackrel{\measuredangle K}{12}~\hfill \stackrel{\measuredangle L}{9(12)\implies 108}~\hfill \stackrel{\measuredangle M}{10(12)\implies 120}[/tex]
