This calculator does not have regression (or CDD).
However, the Forum has extraordinary examples linear and nonlinear human regression in the form of CDD.
http://web2.0calc.com/questions/search/?q=by%3Ahappy7
http://web2.0calc.com/questions/search/?q=by%3Acue123smile
Hopefully Melody and CPhill can cure it before they succumb to it, themselves.
happy7,
The asker wants to know how to find (a) (what does a =).
Where is that answer, happy?
Cue123smile gave Melody (CDD) Contagious Dumbness Disease
http://web2.0calc.com/questions/how-many-different-ways-can-55-cents-change-be-given-using-nickels-and-or-dimes#r5
Now happy7 gave it to Brittany. (Stay on guard, Brittney. It is very contagious!)
It looks like CDD causes grade inflation, too. That is why you passed with 80%. You have posted several wrong answers that have never been corrected, so 20% would be a more accurate mark.