Real Life: Your family is planning a 7 day trip to Arizona. You estimate that it will cost $300 per day in Phoenix and $675 per day in the Grand Canyon. Your total budget for the 7 days is $2850. How many days should you spend in each location?
time spent in Phoenix  +  time spent in the Grand Canyon  =  total vacation time 
daily rate in Phoenix  *  time spent in the Grand Canyon  +  daily rate in Phoenix  *  time spent in the Grand Canyon  =  total 7 day budget 
HINT: Translate the problem into relationships and variables. In this case, let x represent the number of days spent in Phoenix and y represent the number of days spent in the Grand Canyon.
x + y = 7 300x + 675y = 2850
