I want to send an specific email if in my multiply option check box one option is selected.

So let's say 

if checkbox option 3 is selected I send an email with "x" content

if checkbox option 15 is selected I send an email with "z" content

if checkbox option 4 and 6 and 10 selected I send an email with "a, b, c" content

I cannot find any reference on how to build this code in

I have choosen "if"

than put 

input.checkbox optiom_3 = true

but it is not the right code.

Can you please help how to refer to and apply condition "if" if a multiply checkbox option is selected?