I believe the answer would be 22 degrees. We know that a triangle is 180 degrees. We also know that the box in the corner indicates a right angle which is 90 degrees. 
Knowing that there is a 68 degree angle as well would allow us to add up the two angles and subtract from there to get the answer of the missing angle. 
68+90= 158
180-158=22
I hope this helped. Have a nice day.