10c+2t=$300
20c+4t=$600
8c+4t=$360
Now you have both variables with the same number of tables so that you can effectively find out the cost of the chairs.
600-360=240
since 20-8 is 12,
12c=$240
1 chair costs 240÷12= $20
1 chair costs $20.
since 10c+2t=$300,
$200+2t=$300
and 2t costs $100.
hence 1 table costs $50.
if you want to rent 12 chairs and 3 tables,
12×20 is $240
100×3 is $300.
In total you need 300+240 = $540
