$150/hr is the maximum of the range they give, and then you have to subtract payroll taxes, equipment, marketing, etc. On top of that, it's not like plumbers are working jobs back to back 40hrs a week.
I'd be surprised if the take-home on $150/hr is even close to $60/hr.
Are you just making up numbers? You've asked for sources, other commenters (including myself) have provided several, and the sources disagree with what you're stating spectacularly. I'm baffled by how confident you're being about something that, as far as everyone can currently tell in this thread, is plainly incorrect.