Calculator App for Mac OSX

Mac OSX allows you to type in math equations using spotlight. For example, you can type in "(7*5)+3" and spotlight will return 39. I want to create a similar calculator app that can be accessed from the system tray and the "today view". (The system tray view should appear on click or a keyboard shortcut.) The app should be able to all for adding variables to the equation as well. For example, a user should be able to enter "x+5 = 7" and the app return "2". I have provided two mockups for each view. There is a data entry portion at the top, and recent solved equations will be listed below (with the ability to individually delete recent entries). Please note: I am very picky about the appearance of the final app.