Answer:
Step-by-step explanation:
3x+x-2+x-4+x-6+x-8+x-10+x-12=156
9x-42=156
9x=156+42
9x=198
x=198/9
x=22 is the number of blocks in the first 3 rows.
then you'll have:
20,18,16,14,12 & 10 in each successive row.
proof
3*22+20+18+16+14+12+10=156
66+90=156
156=156