c# - adding integer and to an hours value -

i have combobox has values 1-25.
have 2 datetimepickers display time values.

if choose 10:00 am first datetimepicker , 2 combobox, i'd result 12:00 pm in second datetimepicker.

how can done?

seconddatepicker.value = firstdatepicker.value.addhours(convert.toint32(combobox1.selectedvalue));