News Miner by Jeff Richardson.  Jim Plaquet has crunched the numbers, and he presents a few pieces of scratch paper filled with tiny handwritten figures to prove it.  Contractors, welding shops, trucking companies and more — they’ve all seen an employment boost since the Legislature passed Senate Bill 21, its industry-friendly overhaul of the state’s oil tax structure. Last winter — the first production season since the new system was signed in 2013 — included a hiring spike that hasn’t been seen in years, he said.