There are 8436 steel balls, each with a radius of 1 cm, stacked in a pile, with 1 ball on top, 3 balls in the second layer, 6 in the third layer, 10 in the fourth and so on. the number of horizontal layer on the pile is Choose the correct choice from the following:
A) 34	B) 38	C) 36	D) 32	E) None
Explanation :   Assume the number of layers in horizontal pile is n.   So, Σn(n+1)/2 = 8436.   =&gt; (1/2) [ Σn2 + Σn ] = 8436.   =&gt; n(n+1)(n+2)/12 +n(n+1)/4 = 8436.   =&gt; n(n +1) [(2n + 4) / 12 ] = 8436.   =&gt; n(n +1)(n+2) / 6 = 8436.   =&gt; n(n +1)(n+2) = 36 x 37 x 38.   So, n=36.   Answer : 36
<result>C</result>
There are 8436 steel balls, each with a radius of 1 cm, stacked in a pile, with 1 ball on top, 3 balls in the second layer, 6 in the third layer, 10 in the fourth and so on. the number of horizontal layer on the pile is