Question 609738
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.
{{{6624/2880 = 2.3}}} cans of sealant would cover all 12 blocks.