A manufacturing company in charge of selling welding equipment owns 3 different brands of welding equipment. Let X1, X2 and X3 be random variables which represent the monthly sales volume for each equipment. If X1, X2 and X3 are independent normally distributed random variables with means $8,000; $15,000; and $12,000 and standard deviations $2,000 ; $5,000 ; and $3,000, respectively. Obtain the probability that, for a particular month, the total sales volume for the three welding teams is greater than $50,000.