Sam bought 12 boxes x $10 = $<<12*10=120>>120 worth of highlighters.
He bought 12 * 30 = <<12*30=360>>360 highlighters in total.
Sam then took 5 boxes × 6 highlighters/box = <<5*6=30>>30 highlighters.
He sold these boxes for 5 * $3 = $<<5*3=15>>15
After selling these 5 boxes there were 360 - 30 = <<360-30=330>>330 highlighters remaining.
These form 330 / 3 = <<330/3=110>>110 groups of three pens.
He sold each of these groups for $2 each, so made 110 * 2 = $<<110*2=220>>220 from them.
In total, then, he earned $220 + $15 = $<<220+15=235>>235.
Since his original cost was $120, he earned $235 - $120 = $<<235-120=115>>115 in profit.
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