Question 15469
Sum of angles of triangle=180 degrees.
Let x= first angle. 
So:x+(x+21)+(x-15)=180 Now solve equation
Adding the terms gives:3x+6=180 Subtract 6 from both sides
3x=174 Divide both sides by 3
x=58 So:
1st angle = 58 deg.
2nd angle = 58+21=79 deg.
3rd angle = 58-15=43 deg.

Pete