90
6+6=12
12+8=20
20+10=30
30+12=42
42+14=56
56+16+18=90
1+1+2+2+3+3+4+4+5+5+6+6+7+7+8+8+9+9+0+0 would equal to 90 if you break it down.
Hope this helps!
Have a great day :)
