Looking to copy multiple relative references in a single formula.

Basically, the first part of my formula is to multiply the value of two cells if the value of a 3rd cell is "Y", otherwise read 0. (=IF(D1="Y",A1*C1,0)). That's the easy part. What I really want is one cell to add up about 40 columns worth of the same expression. (=Sum(If(D1="Y",A1*C1,0),If(D2="Y",A2*C2,0),...,If(D40="Y",A40*C40,0)).
I'm wondering if there is a way to simplify creating this formula without having to build the entire thing by hand. It seems like there should be a function similar to the relative returns you automatically get when dragging a formula down or over, but one that allows me to populate those relative numbers into a single formula.
Sorry if there are any typos in my formula, I'm doing this on my phone. The formula itself works, I'm just looking for a way to shorten the process of writing it.

Thanks

Awesome, thanks so much