You can put this solution on YOUR website!
Your first part is correct:
The total surface area of one of the blocks is 552 sq.in.Now 1 can of sealant covers 20 sq.ft.
And 20 sq.ft. = 20*144 = 2880 sq.in. because there are 144 sq.in. in one sq.ft.
So each can of sealant covers 2880 sq.in.
For the 12 blocks, the total surface area is: 552*12 = 6624 sq.in.
So you need to divide the total surface area to be covered, that's 6624 sq.in by the coverage for one can, that's 2880 sq.in.
cans of sealant would cover all 12 blocks.