Hey,
You can see that the line next to both angles is straight, so it is equivalent to 180 degrees. This means both other angles are supplementary (they add to equal 180). Therefore, 78 + (5q+2) = 180.
Here are the steps to solve:
1) Subtract 78 from the 180 total.
180 - 78 = 102
2) Reassign the value of the variable term
5q+2 = 102
3) Subtract 2 from both sides.
5q = 100
4) Divide by 5
q = 20
And there you go!