So far today:

[adric]

• Conceived some trivial Scheme functions as part of working through HtDP through 3.0
• Made coffee poorly.
• Wrestled HP 3210 all-in-one (eg this) into functionality (printed, scanned) (This bout was a rematch.)
• Discovered though HtDP 3.1 that I can no longer do simple algebra, as indeed I had previously suspected. That stings a bit.
• Failed to ignore many bad things coming out from the telly.
• Looked over last week's Time including interesting pieces on Twitter and Abrahamic monotheism.
• Noticed that my trusty Ruby OSA scripts are giving Bus Errors.
• Hunted up and pasted in images for the ef soundtrack mp3s I have assembled.
• Determined that the era of crossposting to LJ has come and gone for me.

So, lazyweb, anyone want to explain to me how to find a function that calculates:

At a price of $5.00 per ticket, 120 people attend a performance. Decreasing the price by a dime ($0.10) increases attendance by 15.¹

I tried two equations in two unknowns, substitute one into the other to solve for one variable and promptly got myself lost. Much scribbling and calculations later I confirmed that I was way off. Help?

¹ is excerpted from HtDP 3.1