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 seventh row?
Choose the correct choice from the following options:
A) 13  B) 15  C) 17  D) 19  E) 21

Rationale: "let x be the number of cans in row 1 . the total number of cans is x + ( x + 3 ) + . . . + ( x + 24 ) = 9 x + 3 ( 1 + 2 + . . . + 8 ) = 9 x + 3 ( 8 ) ( 9 ) / 2 = 9 x + 108 since the total is less than 120 , x must equal 1 . the number of cans in the 7 th row is 1 + 3 ( 6 ) = 19 the answer is d ."
Answer: D