Thank you to anyone that helps

Me figure out the process to determine x you appreciate it : )

Jamie is hiking up a small mountain. he climbs up at a constant rate of 300 feet/hour until he reaches the peak at 1,500 feet. after that, he hikes down at the same rate to the base of the mountain. the equation that models jamie’s elevation, e, after t hours is e = . jamie’s elevation will be 600 feet after hours and after hours.

Find the solution of this system of equation -7x+y=-20 9x-3y=36