Questions on General Use of Transistors

Other Hardware General Electronics
12

So then, if I had 42 LEDs and each one draws 20ma, then that that set of LEDs will draw 840ma or 0.84 amps in total. Then using the equation CollectorCurrent = BaseCurrent*CurrentGain

0.84 = 0.04*CurrentGain (Where the 0.04 come from the Arduino's output right? or is it 0.02 from the LED?)

CurrentGain = 21

Now, I might have done that completely wrong, but if I didn't, then do all I need to find is a transistor with a current gain of at least 0.84 amps with a current gain of at least 21 hfe?