Can someone help with this please?

<4 = 81

Step-by-step explanation:

we know that all the interior angles of a triangle will equal 180

so <1 + <2 + <3 = 180

we know that <4 is the exterior angle to <3

the exterior angle is equal to the angles opposite to its interior

<3 is the interior angle to <4

<1 and <2 are the angles opposite to <3

so <4 = <1 + <2

<4 = 42 + 39

<4 = 81

i'm assuming that it's c.)   volcanoes built the mountains and earthquakes tore them down.