Hard Matchstick Puzzles

#588: Fix 5+4=70 hard #589: Fix 0-8=9 hard #591: Fix 2-8=8 hard #592: Fix 9+8=76 hard #593: Fix 9-2=17 hard #594: Fix 6-7=12 hard #595: Fix 6-5=10 hard #596: Fix 2+0=70 hard #599: Fix 7-4=17 hard #600: Fix 8-7=9 hard #601: Fix 8-4=13 hard #602: Fix 9-6=16 hard #604: Fix 8-9=77 hard #606: Fix 9-1=18 hard #612: Fix 5-4=8 hard #615: Fix 9-5=74 hard #619: Fix 2-8=18 hard #622: Fix 8+5=74 hard #623: Fix 8-6=13 hard #626: Fix 6+2=70 hard #627: Fix 0+9=77 hard #631: Fix 3-7=70 hard #641: Fix 4-2=8 hard #643: Fix 5+6=72 hard #647: Fix 8-3=12 hard #651: Fix 8-3=71 hard #655: Fix 3-7=18 hard #657: Fix 9-8=15 hard #661: Fix 4+1=71 hard #672: Fix 1+4=71 hard #676: Fix 5-8=14 hard #678: Fix 9-9=78 hard #679: Fix 7-6=73 hard #680: Fix 2-8=2 hard #683: Fix 8-2=70 hard #686: Fix 4-8=13 hard #692: Fix 8-0=9 hard #698: Fix 5+7=73 hard #699: Fix 8+9=71 hard #703: Fix 2+9=70 hard #705: Fix 6+8=0 hard #708: Fix 7-5=72 hard #712: Fix 8-6=74 hard #717: Fix 4-8=10 hard #718: Fix 3-8=17 hard #720: Fix 7-7=74 hard