Question 24532
Let the first angle be A, the second angle be B and the third angle be C.
From the problem description, you can write:
A = B-9
C = B+3

And you already know (or should know) that for any plane triangle: A+B+C = 180 degrees.

So, in A+B+C = 180, substitute for A and C the first two equations:

(B-9) + B + (B+3) = 180 Simplify and solve for B.
3B - 6 = 180 Add 6 to both sides of the equation.
3B = 186 Divide both sides by 3.
B = 62
A = B-9
A = 62-9 = 53
C = B+3
C = 62+3 = 65.

The three angles are:
A = 53 degrees.
B = 62 degrees.
C = 65 degrees.