Instruction 6.2 John Has Two Jobs. for Daytime Work at a Jewellery

Short Answer

Instruction 6.2
John has two jobs. For daytime work at a jewellery store he is paid $15,000 per month, plus a commission. His monthly commission is normally distributed with mean $10,000 and standard deviation $2,000. At night he works as a waiter, for which his monthly income is normally distributed with mean $1,000 and standard deviation $300. John's income levels from these two sources are independent of each other.
-Referring to Instruction 6.2,John's commission from the jewellery store will be between what two values symmetrically distributed around the population mean 90% of the time?