Direction.
The lengths of the components (X₁, X₂, and X₃, respectively) are normally distributed. If the mean length of the components are µ₁=µ₂=µ₃ =100 mm and variances are σ₁₂=σ₂₂=σ₃₂=12.

Calculate:
The probability that the total length of the three components is less than 309 mm