Question

Please help me ASAP!! And don’t give me a fake answer so you can get points

Answer 1

Since the $n$-th level requires $n$ block, she'll need a total of

$1+2+3+4+5+6+7+8+9+10+11+12$

blocks. This computation can be done quickly if one remembers that the sum of the first $n$ numbers equals

$\dfrac{n(n+1)}{2}$

Plugging $n=12$ we get

$\dfrac{12\cdot 13}{2}=6\cdot 13 = 78$