How do I create object every other time

Hello,

I am facing one problem and can't solve for a last few days (I am new to c2), I do have appearing scrolling object coming from a right and it is always a same sprite every 3 seconds. what I want to do it is to create power up10 pixels above it. I have managed to do so for every obstacle appears but I want to appear for every 10th or 20th etc. I tried to set time to appear every 6 seconds (to appear on every second obstacle gets created) but it does come up on one behind a player as there is always two visible obstacles on a screen. So how do I make power up to come up in a front obstacle. sorry for my grammar. Thanks

you could have the object spawn the powerup..

or every time an object is created add 1 to a variable and if the variable is what you want create the powerup in the same event but after creating the object..