if choose something in drop down then checkbox is checked

I want to pick from a list in the drop down.  Depending on what is choosen then a box will be checked automatically.  This

is what I have so far for script.

if (dropdown == "blah") then this.rawValue = 1

I am not sure if it should be JavaScript or FormCalc...I assume JavaScript since there is no calculation.  I am also unsure whether to put the script on the dropdown box or the checkbox.  Also which event do i use?

Thanks