Before after select event validation and results with jquery

Question

I am using a javascript function (F) (jquery )which uses 3 select values selected by the user to calculates a value - R(result)

R is a number ranging from (1 through 9), (11) and (22);

I need 2 extra steps one before the calculation and one after.

a. Before calculation takes place: Make sure all three select values are changed before function(F) takes place. If not prompt the user with a notice ( create dom element/ I am using jquery)

b. After the value R is calculated show an element corresponding to the result e.g. if R is 1 show an element ( a predetermined "link" element corresponding to each result value)

thanks a lot.