Determine the value of x. can someone ? explain steps on how to do this?

Angles on a straight line always adds up to 180°

The angle on the left side of 100° is, (180-100) = 80

Do the same with 80° and the angle beneath it (Remember! angles add up to 180° on a straight line).

Hence, 180 - (x+105) = 80
=> 180-80 = x+105
=> 100-105 = x
x = -5

Need more information to solve it