$fn = 100;
difference() {
  cube([15,15,20], center=false)  ;
  translate([2,2,2]) cube([11,15,21], center=false) ;
  translate([-4,17.5,-2]) rotate([35,0,0]) cube([25,15,30], center=false) ;  
  translate([7.5,6,12.5]) rotate([90,0,0]) cylinder(h=10,d=4.5, center=false) ;    
  translate([7.5,9,-4])   rotate([0,0,0])  cylinder(h=10,d=4.5, center=false) ;    
}