If condition for combobox, I select 1 value from combo box1

Question

If condition, When I select one value from combo box1, then just related value will show in combo box2. I have 2 combo box. Combo box 1 have value formalLeave, casualLeave. And combo box 2 have days value such as 2,3,4 days. But when I select the employee id, combo box1 show 2 category and combo box2 show every inputed day, such as 1,2,3. But I want to select just 1 value from combo box1 then the Selected related day will show in combo box2.