The following creates an object with two slots:
translate([-40,-40,0]) difference() {
cube ([90,28,12]);
translate([12,-.01,5]) cube([12.7,28.02,14.02]);
translate([65,-.01,5]) cube([12.7,28.02,14.02]);
How can the first main cube be extended to be a complex object of the syntax:
cube([60,20,10],center=true);translate([0,0,5])cube([30,20,10],center=true);
and then use difference
to create holes?