Fraction of the land is used to grow tomato plants=1-(fraction of the land to grow potatoes + fraction of the land to grow spinach)
Land used for to grow tomato plants=1-(3/7 + 2/5)
=1-(15+14)35
=1-29/35
=(35-29)/35
=6/35
Answer: this organic far uses 6/35 of the land to grow tomato plants.