Calculation of Maximum Root Mean Square of the Error Source

"The maximum 3-sigma error for a system is 30. There are 3 additive independent error sources. One (X) is uniformly distributed in the interval 2-10. A second (Y) is exponentially distributed with A Lambda =.5 What is the maximum RMS value of the 3rd error source (Z)? Recompute the result if the error model changes to T= 2X+3Y+Z. Interpret this result. "