SAT Question fd8745fc: Lines, Angles, and Triangles answer and explanation with Desmos solution

The sum of the measures of the interior angles of a triangle is $180^{\circ }$. It's given that in triangle $JKL$, the measures of $\angle K$ and $\angle L$ are each $48^{\circ }$. Adding the measures, in degrees, of $\angle K$ and $\angle L$ gives $48+48$, or $96$. Therefore, the measure of $\angle J$, in degrees, is $180-96$, or $84$.