4. Last Sunday, the 101 Avenue rock band sold a total of 40,000 tickets for their concert at a local arena with proceeds totaled $1,550,000. Tickets can be bought
in one of three ways: a ground level seat costs $55, a mid-level seat costs $45. and
an upper-level seat costs $30. The number of tickets sold for upper level seats is
equivalent to the sum of the number of tickets sold for ground and mid-level seats
combined. Define variables and write systems of equations to represent the
situation.