The organic farm uses 3/7 of the land to grow potatoes
 => 2 /5 of the land to grow spinach
 => x = the fraction of the land to grow tomato plants.
 The easiest wat to get the answer is convert first the fraction to decimals
 => 3/7 = 0.43
 => 2/5 = 0.4
 => x = ???
 => 0.43 + 0.4 = 0.83
 => let the whole land = 1 
 => 1 – 0.83
 => 0.17, the remaining land left for tomato plants
 Convert now to fraction
 => 17/100 (Approximately)
YOu can also use this method:
=> 3/7+ 2/5 +x = ?
Find the LCM
=> 3/7 + 2/5 = 29/ 35
=> 35/35 - 29 / 35
=> 6 / 35, the remaining land