Instruction 6-4 John Has Two Jobs.For Daytime Work at a Jewelry Store

Short Answer

Instruction 6-4
John has two jobs.For daytime work at a jewelry 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 6-4,John's commission from the jewelry store will be between what two values symmetrically distributed around the population mean 90% of the time?