For this case what we must do is take into account that the angle can be measured in two ways starting from the positive x axis. 
- 1) Counterclockwise 
- 2) Clockwise direction 
We have then that the measures between both lines are given by: 
1) Counter-clockwise: 90 degrees 
2) Clockwise: -90-90-90 = -270 degrees 
Answer 
two possible measures of the angle below are: 
-270 ° and 90 °