Total of all angles should equal 360 degrees. So 360-132-68-66=94, angle F is 94 degrees.
Well, 25 certainly doesn't divide evenly into 595, but it does divide into 600, which is <em>very</em> close to 595. So if we divide 600 by 25, we can get a rough estimate of what 595 divided by 25 is.
The function will be

where y is the balance, and x is the number of month.
The raph will be a line on the xy-plain which starts at the point (0, 360), and end in the point (72, 0).
Hope it helps.