78×58-28-78=78×58-28-72-6=(80-2)×58-(28+72)-6=80×58-2×58-100-6=80×(60-2)-116-106=80×60-80×2-222=4800-160-222=4800-382=4418
78X78=78X(80-2)=78X80-78X2=6240-156=6084
