David and Sammy had each 840 tree seedlings. David planted equal number of seedlings per row in x rows while Sammy planted equal number of seedlings in (x + 1) rows. The number of tree seedlings planted by David in each row were 4 more than those planted by Sammy in each row. Calculate the number of seedlings David planted in each row.
(840 / x) = [840 / (x + 1)] + 4 ... 210 / x = [210 / (x + 1)] + 1
210 x + 210 = 210 x + x^2 + x ... x^2 + x - 210 = 0