Add a variable in string

<img src="http://track.opicle.com/aff_l?offer_id=2193&adv_sub=LEAD_ID" width="1" height="1" />

var x ; 

x Should be replace at the place of LEAD_ID


<img src="http://track.opicle.com/aff_l?offer_id=2193&adv_sub=x" width="1" height="1" />

Meas var x will replace at the place of Lead_ID