In a certain supermarket, a triangular display of cans is arranged in 9 rows, numbered 1 through 9 from top to bottom. Each successively numbered row contains 3 more cans than the row immediately above it. If there are fewer than 120 cans in the entire display, how many cans are in the six row?
Choose the correct answer
A) 12
B) 14
C) 16
D) 18
E) 20
Let x be the number of cans in row 1.   The total number of cans is x + (x+3) + ... + (x+24) =   9x + 3(1+2+...+8) =   9x + 3(8)(9)/2 =   9x + 108   Since the total is less than 120, x must equal 1.   The number of cans in the 6th row is 1 + 3(5) = 16   The answer is 16.
<result>C</result>
In a certain supermarket, a triangular display of cans is arranged in 9 rows, numbered 1 through 9 from top to bottom. Each successively numbered row contains 3 more cans than the row immediately above it. If there are fewer than 120 cans in the entire display, how many cans are in the six row?