A triangle is 180°. So you can do:
3.2n + 6.4n + 2.4n = 180 Simplify
12n = 180
n = 15 Now that you know the value of n, you can plug it into each individual angle/equation
∠X = 3.2n plug in 15 for n
∠X = 3.2(15)
∠X = 48°
∠Y = 6.4(15)
∠Y = 96°
∠Z = 2.4(15)
∠Z = 36°