Hemodynamic model with mutiple conditions

Hi all,

In task fMRI, I have three stimulus conditions with “the same trial number”. I want to make a hemodynamic model to enhance one condition and diminish the effect of two other conditions.
which mathematical multiplication of hemodynamic response is right?
1- cond1 - cond2 - cond3
2- cond1 - 0.5cond2 - 0.5cond3