The three angles must add up to 180 degrees.
x - 39 + x - 29 + x = 180 Collect like terms on the left
3x - 68 = 180 Add 68 to both sides.
3x = 180 + 68
3x = 248
x = 248 / 3
x = 82.66667
Answer
x = 82,666667 for the largest angle
x - 29 = 53.666667 for the medium size angle
x - 39 = 43.666667 for the smallest size angle