## Geometry: Common Core (15th Edition)

$H$
We will use the triangle sum theorem to find the measure of the third angle. The triangle sum theorem states that the measure of all three interior angles of a triangle equal $180^{\circ}$. Let's set $x$ equal to the measure of the third angle and set up the equation: $43 + 38 + x = 180$ Add the constants on the left together: $81 + x = 180$ Subtract $81$ from each side of the equation to solve for $x$: $x = 99$ The measure of the third angle is $99$. This corresponds to option $H$.