Question 76679
Let x=number of adult tickets sold
Then 120-x=number of child tickets sold

Now we are told that the receipts for adult tickets ($20x) plus the receipts for child tickets ($8(120-x)) equals $2040.  So our equation to solve is:

20x+8(120-x)=2040  get rid of parens

20x+960-8x=2040  subtract 960 from both sides
20x+960-960-8x=2040-960  collect like terms
12x=1080  divide both sides by 12

x=90-----------------------------number of adult tickets sold

120-x=120-90=30--------------------number of child tickets sold

ck

20*90+8*30=2040
1800+240=2040
2040=2040

also 90+30=120
120=120

Hope this helps-----ptaylor